PRACTICAL 

ELECTRICITY 



PUeUSHED BY 



CLEVELAND ARMATURE WORKS. 




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COPYRIGHT DEPOSIT. 



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PRACTICAL 
ELECTRICITY 



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WITH 

QUESTIONS /^ANSWERS 

THIRD EDITION 

COPYRIGHTED 



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THE LIBRARY OF 
CO'^GRESS. 

Two Cor-ca Received 

AUG. 17 1901 

COPvRtGHT ENTRY 

ICLASS /^.XXc. Nn. 
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INTRODUCTORY. 



In March, 1896, The Armature Winder made its first appear- 
ance, its attractive feature being the commencement of a series of 
lectures on designing dynamos and motors, these letters being 
written from daily shop practice, and made comprehensible hv 
questions and their subsequent answers. As each paper with its 
lecture made its appearance, the interest manifested by readers 
became more pronounced, until we were flooded with inquiries for 
numbers which the various readers had missed. As we had only 
reserved a very few papers of each issue, our ability to supply 
the back numbers was limited. We consequently decided to 
print the lectures in book form, and so notified our readers of 
this decision, with the result that orders for the book came in, in 
quantities which were beyond anything We had anticipated. 
This evidence of the popularity of our efforts encouraged us in 
compiling a work much more extensive and valuable than had at 
first been our intention. In ord^er to accomplish this, we felt the ne- 
cessity of associating with us a man of greater technical knowledge 
than we ourselves possessed, so that the work might be thoroughly 
criticised and enlarged. We selected Mr. John C. Lincoln, an 
electrical engineer of national reputation, who has contributed 
articles to this book covering matters of great interest, and, so far 
as we have been able to learn, ideas never before appearing in 
print. 

CLEVELAND ARMATURE WORKS. 

Cleveland, Ohio, July 1, 1901. James L. Mauldin \ 

AlVIN a. PlFER [PROPS. 



PBEFACE. 

This book was T^ritten especially lo assist those who 
have some practical knowledge of electricity and who wish 
to learn more of the way in which wiring is calcnlated and 
of the simpler and more important parts of dynamo electric 
machme desig-n. Some of the methods used and explana- 
tions advanced in the book are, so far as the writers know, 
entir':^!y new, and it has all been written with the idea of 
illnstrating" the subject and making- it las simple and as easy 
of comprehension as possible. The only way to obtain a 
working knowledge of the subje^ct is by careful study. The 
book has been arranged so that those who are willing to 
devote some effort to the w^ork can get a clear conception 
of the m.ore importlant ideas and laws that underlie the sub- 
ject. One who studies the text and answers the questions 
at the end of each chapter should be able to calcuhite a 
wiring job for liofhts or power; to calculate the proper size 
and amount of wire for a dynamo when he has the dimen- 
sions of the miachine; to calculate the size and winding for 
a magnet to give a required pull, etc. 

The table of contents shows the scope of the work. 

The qiiestions which follow each chapter, in connection 
with the answers, will bring out the more important points 
treated in each chapter. It is believed that a careful study 
of the text and the working of the examples will serve to 
throw a great deal of light upon a subject in which a great 
many people are interested. The dictionary in connection with 
this work is a valuable feature. 

Houston's Electrical dictionary was largely used in the 
preparation of same. 

CLEVELAND ARMATURE WORKS. 

July 1, 1901. CLEVELAND, OHIO. 



TABLE OF CONTENTS. 



CHAPTER I. Wiring. 

II. Electric Batteries. Electro Plating. 

III. Magnetism. 

IV. The Magnetic Circuit. 
" V. Magnetic Traction. 

" VI. Magnetic Leakage. 

" VII. Energy in Electric Circuits. 

" VIII. Calculation of Size of Wire for Magnetizing Coils. 

IX. Calculation of E. M. F.'s in Electric Machines. 

X. Counter E.M.F. 

" XI. Hysteresis and Eddy Currents. 

*' XII. Armature Keaction. 

'* XIII. Sparking. 

" XIV. Winding of Dynamos and Motors. 

" XV. Proper Method of Connecting Dynamos and Motors. 

Self Excatation. 

" XVI. Diseases of Dyn^^mos and Motors, their Symptoms and 

how to cure them. 

" XVII. Arc and Incandescent Lamps. ' 

" XVIII. Measuring Instruments. 

*' XIX. Alternating Current. 



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CHAPTER I. 
WIKIJMG. 

1. It is very commonly said that nothing is known of 
electricity. This is both true and false. We do not know 
what electricity is nor anything of its ultimate nature, but 
we do know a great deal about the laws which govern the 
action of electricity. 

For all ordinary purposes the action of electricity is 
very closely analo{>'Ous to that of water. From the 
study of the principles which govern the flow and action of 
water a very great deal can be learned concerning the prin- 
ciples and laws governing the action of electricity. 

In this analogy the water represents electricity. When 
water flows from a higher to a lower level, it is capable of 
doing work by driving some kind of a water wheel. The 
greater the height through which the water falls, the 
greater the amount of work it can do. The same thing is 
true of electricity. The greater the difference in electrical 
level, or difference of potential, or the greater the voltage, 
the greater the amount of electrical work the electricity can 
do. The unit of difference of electrical level is the volt, and 
we may say that the volt corresponds to one foot of "head" 
in a system for developing power by water. The amount of 
power that can be developed from a water fall depends on 
two things; first, the fall in feet or the head, and second, 
the size of the stream. At Niagara Falls the power that can 
be developed is practically infinite, not because the height 
of the fall is so great, but because the size of the stream is 
so great. Any water fall is capable of developing power, 
depending on the size of the stream. The unit of flow may 



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be taken as one gallon per second. The corresponding 
quantity in electricity is called current. The unit of cur- 
rent is called the ampere. The ampere then corresponds to 
the one gallon per second in a flow of water. 

The amount of water that can flow from a higher to 
a lower level depends on the size of the pipe line through 
which the water is led. Imagine a large pond of water 
twent3^-five feet above the sea. The amount of water that 
will flow from the pond through a 4-inch pipe is very much 
greater than what will flow through a ^-inch pipe. Again 
if there are two pipes of the same size leading from the 
pond to the sea and one is twice as long as the other, aToout 
twice as much water will flow through the short pipe as 
through the long one. The friction of the water is greater 
in the long pipe, or the resistance to the flow is greater, and 
so less water flows. 

There is no convenient unit for the resistance of a pipe 
to the flow of water, but the unit of resistance of a wire to 
carrying a current is well defined and is called the ohm. 




Figure 1 

Resistaruro ofTcTod to flow of water tliroiij^h a Iotijj: orookod pipe. 
Discharge in gallons per minute corresponiiing to amperes. 



The, resistance offered by the long", small, <*rooked pipe 
to the flow of the water corresponds to the resistance of- 
fered by a wire to the flow of the electrical current. An in- 
spection of Fig. 1 will show that the flow depends on the 
head. If, -instead of having a head of 25 feet, it was in- 
creased to 50 feet, the amount of water discharged would be 
doubled, so that the flow depends on the head or pressure. 
If on the other hand the discharge pipe was made larger, 
or shorter, even with 25 feet head, twice as much water 
could be made to escape, so that the flow or current is in- 
versely proportioned to the resistance. 

Putting this in the form of an equation we have: 
Discharge or current equals head or pressure divided 
by resistance or friction. In a circuit carrying electricity 
the same thing is true and we have: Electrical discharge or 
current equals electrical head or pressure, divided by elec- 
trical friction or resistance. Since the unit of electrical 
current is the ampere, and the unit of electrical pressure is 
the volt, and the unit of electrical resistance is the ohm, we 
have: Amperes equal volts divided by ohms, or putting it in 
the form of a fraction we have; 

volts' 
Amperes equals 



ohms 



This relation is known as Ohm's law and is one of the 
most important that we shall consider. Since the electrical 
pressure is what, causes the movement of the electrical cur- 
rent, it is called electro-motive force, and as this term is 
very long it is :ibbreviated to E. M. F. Since the amperes 
measure the amount of flow of electricity, such flow is 



called current, nnd this is abbreviated to C. Kesistance is 
abbreviated to K., nnd ^^e l)ave our Ohms law 

E. M. F. E 

C equals U); or C equals — 

R R 

when E. is used in place of E. M. F. 

By the way in which Ohms law was deduced it is plain 
to see that is is only one form of a general and universal 

law. 

Ohms law is the statement for electrical quantities of 
the general law that the result produced is proportional to 
the eifort expended, and inversely proportional to the re- 
sistance to be overcome. 

To get a general idea of these units we may say that a 
single cell of storage battery has a voltage of two volts. 
One hundred and ten volts is the electrical pressure usually 
employed for lighting incandescent lamps. Two hundred 
and twenty volts is very frequently used as the E. M. F. for 
driving motors. Five hundred volts is universally used on 
street railroads to propel street cars. An ordinary gravity 
battery, such as is usually employed for telegraphic work, 
has an E. iSf. F. of one volt. Dynamos for electrotyp- 
ing usually employ two or three volts. Dynamos for elec- 
troplating from five to ten volts. 

The current taken by an incandescent lamp is about 
1/2 ampere. The current required by a street arc lamp is 
from ten to six amperes, depending on the bi^illiancy of the 
light. The current used in a land telegraph wire is .003 to 
.005 amperes. The resistance of 1,000 feet of copper wire 
one-tenth of an inch in diameter is one ohm. Ten 
feet of German silver wire the size of the lead ^ in 
a pencil has a resistance of one ohm. The resist- 



ance of a mile of the heavy feed wire used 
propelling" street cars is about one-tenth of an ohm. 



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Figure 2 
System for distributing hot water at constant pressure. 

Suppose Fig. 2 to be part of the heating* system of a 
building. The pump takes in the water from 
the low pressure pipe, and after passing 
through a heater it is forced out into the 
high pressure pipe to the radiators over the building. If 
the pipes PI and PO are large enough there wdll be the same 
pressure practically at all parts of the pipe, and each radia- 
tor Rl, R2 and R3 will be exposed to the same pressure and 
receive the same amount of water provided they are simi- 
lar. If, however, the pipes PI and PO are small, some of the 
pressure on the water in the pipe PI will be lost in over- 
coming the friction of the pipe, so that radiator R3 farthest 
away from the pump would not get the same amount of 
pressure as Radiator Rl nearest the pump. There would be 
a similar loss of pressure in pipe PO. If the pump produces 
a pressure of twenty pounds per square inch, and the fric- 
tion and resistance of the leading pipe PI is great enough 
to cause the pressure to fall to 19 pounds at the nearest 
radiator Rl, and causes it to fall to 18 pounds at R3, the 



loss of pressure will be two pounds at 113 in ihe pipe PO, 
and two pounds in the pipe PI, if both PI and PO are of the 
same size. The loss will be one pound at El in each pij)e. 
Under these circumstances the pressure driving water 
through III is 18 pounds and through R3 is 16 pounds, in- 
stead of 20 pounds as produced by the pump. Such a sys- 
tem for distributing water is closely analogous to a con- 
stant potential or constant electrical pressure system for 
distributing electricit3\ The pump takes the water from 
one main pipe and raises the pressure and delivers it to the 
other pipe. The radiators between tliese pipes receive the 
water at practically constant pressure. The total stream in 
the main pipe is the sum of the individual currents in the 
radiators. The loss of head or pressure in the main pipes is 
greater as the flow of water is increased, and, if the radia- 
tors reqTiire practically constant pressure to work properly, 
soon reaches a limit. In each of these four respects such a 
water system is perfectly analogous to a constant potential 
lighting system. The pump corresponds to the dynamo in 
Fig. 3. which takes the electricity from one wire and raises 
its pressure so that it is 110 volts higher at one side of the 
dynamo than at the other. 



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Figure 3 
System for distributing electricity at constant pressure. 



The electricity is carried along the main wires Ml and 
MO, which correspond to the two pipes PI and PO in Pig. 
2, to the incandescent lamps LI, L2, L3. It is evident that 
there is some loss of pressure in carrying the current along 
the main wires MO and Ml from the dynamos to the lamps, 
and that this loss of pressure depends on the amount of cur- 
rent or upon the dumber of lamps in use. 

The lamp L3 will get in any case some less pressure 
than the lamp Ll, and when this difference becomes great 
enough so that L3 burns perceptibly dimmer than Ll, 
the main lines Ml and Mo are carrying more current than 
they properly can. In practice the number of radiators in 
such a heating system as shown in Fig. 2 would not probably 
be much over 100, and usually very much less, while for the 
electric system the number of lamps on the dynamo will 
be from five to ten times as great. . 

M, . 




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Figure 4 
Typical constant potential system. 



Fig. 4 shows the dynamo taking current from the main 
MO and delivering it at 110 volts higher pressure to the main 
Ml. Part of it leaves the main Ml for the branch 131 and 
flows through the seven lamps to the other main MO. The 



8 

voltage is lost in overcoming the resistance of the lamps. 
The resistance of -th-e lamps constitutes from 90 to 98 per 
cent, of the resistance of the circuit. A second part leaves 
the main at B2 and passes into the wires of this branch 
through the 17 lamps shown. The rest of the current 
passes to B3 and through the 8 lamps in that circuit. There 
will, of course, be some loss of pressure or "drop" in the 
branch circuits. 

The calculation required in wiring is needed to find 
out how large to make the main wires MO and Ml and how 
large the wire on the branch circuits should 'be. The whole 
system should be so designed that there should be a differ- 
ence of only a volt or two between the various lamps on the 
circuit. The point to be aimed at is even or constant volt- 
age for the lamps. 

We will take up three* different forms of Ohm's law that 
will be convenient for use in calculating wiring problems. 

E. M. F. 

We hav^ seen that C equals , or, put into words, 

R 

amperes equal volts divided b}' ohms. 

The two other forms of this most important equation 
are volts equals amperes multiplied by ohms; or 

E. M. F. equals' C multiplied by R (2) ; and third, ohms 

E. M. F. 

equal volts divided by amperes; or, R equals (3). 

C 

These three equations should be carefully studied and 
memorized. For our work in wiring, the second is the most 



important. Equation (2) means that the loss in volts in 
any part of the circuit depends on the amount of current 
the wire is carrying, and also on the resistance of the wire. 
If the amount of current carried is doubled, the volts lost 
are doubled; and if a new wire is used of twice the resist- 
ance, the loss of volts is doubled, and in general the volts 
lost or the "drop" is equal to the amperes the wire is carry- 
ing multiplied by the ohms of resistance of the wire car- 
rying the current. Suppose there w^ere 100 lamps on the 
three circuits shown in Fig. 4 and that they were very 
close together, so that they all received about the same 
E. M. F. from the mains ^11 and MO, but that the dynamo 
was about 500 feet from the lamps, near an engine. In 
such a case the principal loss of pressure would be in the 
mains carrying current between the dynamo and lamps. If 
we use Xo. 6 wire, which is .162 inches in diameter, there 
would be a resistance of .395 ohms in the mains, for there 
are 1,000 feet in the two mains, and the table No. 1 shows 
this. Each lamp requires Vi ampere, so that 100 lamps "will 
require 50 amperes. 

By formula 2 we have volts lost in leads or mains equal 
amperes multiplied by ohms, or drop, equals 50 multiplied 
by .395 equals 19.75 volts. In this case, if the lamps were 
to be supplied with 110 volts, the dynamo would have to 
produce 110 volts plus 19.75 volts, or 129.75 volts. Circuits 
of this sort are frequent, and if carefully operated such a 
great loss as 20 volts in the mains may be allowed. The 
ordinary case, however, is one in which the lamps are about 
equally distributed between the dynamo and the end of the 
circuit. In such a case a drop of 20 volts in the mains 
would not be permissible, for then the lamps near the 
dynamo would get 130 volts and those at the end of the 



10 

circuit would get 110 volts. This is altogether too much 
variation. The greatest variation that should ever be al- 
lowed is 8 volts, and all well-regulated plants do not have 
more than two. The reason that it is best to have the 
variation a minimum is that the incandescent lamps have a 
much longer life if the voltage is constant than if it is not. 
If a lamp has a life of 800 hours at 110 volts, it will not 
burn more than 200 hours at 115 volts, and if it is burned 
at 105 volts it will not give more than 2-3 of its rated light. 
The drop usually allow^ed in mains for a building does not 
exceed 3 per cent., and in the best plants is not over 2 per 
cent. 

Table 1 gives the properties of copper wire of all the 
American or B. & S. (Brown & Sharpe) gauge sizes. 



TABLE 1. 

PROPERTIES OF PURE COPPER WIRE. 



M ^ 


AT 


75 DEGREES FAHRENHEIT 




m 


a P«C; 










R. Ohms 


■3 


Brow 

ic Shai 
Gaug 


R. Ohms 
per 


Ohms 
per Mile 


Feet 
per Ohm 


Ohms per Lb. 


per 
1000 Feet 

1 . 


•^ 


1000 Feet 








150° 


rt^ ^ ^ 


0000 


.04906 


.25903 


20383. 


.000076736 


.05675 




•000 


.06186 


.32664 


16165. 


.00012039 


.07160 


bcfcc 


00 


.07801 


.41187 


12820. 


.00019423 


.09028 







.09831 


.51909 


10409. 


.00030772 


.1161 


1 


.12404 


.65490 


8062.3 


.00048994 


.1435 




2 


.15640 


,82582 


6393.7 


.00078045 


.1810 


s^^ 


3 


.19723 


1.0414 


5070.2 


.0012406 


.2283 


<! o 


4 


.21869 


1.3131 


4021.0 


.0019721 


.2879 


? 


5 


.31361 


1.6558 


3188.7 


.0031361 


.3630 




6 

7 


.39546 
.49871 


2.0881 
2.6331 


2528.7 

2005.2 


.0049868 
.0079294 


.4577 
.5771 






8 


.62881 


3.3201 


1590.3 


.012608 


.7278 




9 


.79281 


4.1860 


1261.3 


.020042 


.9175 




10 


1. 


5.2800 


1000.0 


.031380 


1.157 




11 


1.2607 


6.6568 


793.18 


.050682 


1.459 




12 


1.5898 


8.3940 


629.02 


.080585 


1.840 




13 


2.0047 


10.585 


498.83 


.12841 


2.320 




14 


2.5908 


13.680 


385.97 


.20880 


2.998 




15 


3.1150 


16.477 


321.02 


.31658 


3.606 




16 


4.0191 


21.221 


248.81 


.51501 


4.651 




17 


5.0683 


26.761 


197.30 


.81900 


5.867 


103.0 


18 


6.3911 


33.745 


156.47 


1.3024 


7.398 


84.0 


ir 


8.2889 


43.765 


120.64 


2.1904 


9.594 


66.0 


20 


10.163 


53.658 


98.401 


3.2926 


11.76 


56.3 


21 


12.815 


67.660 • 


78.037 


5.2355 


14.83 


46.8 


22 


16.152 


85.283 


61.911 


8.3208 


18.70 


39.3 


23 


20.377 


107.59 


49.087 


13.238 


23.59 


33.5 


24 


25.695 


135.67 


38.918 


21.050 


29.73 


27.4 


25 


32 400 


171.07 


30.864 


3:3.466 


37.50 


24.4 


26 


40.868 


215.79 


24.469 


53.235 


47.30 


19.6 


27 


51.519 


272.02 


19.410 


84.614 


59.64 


17.0 


28 


64.966 


343.02 


15.393 


134.56 


75.20 


14.4 


29 


81.921 


432.54 


12.207 


213.95 


94.82 


11.8 


30 


103.30 


545.39 


9.6812 


340.25- 


119.5 


10.0 


31 


127.27 


671.99 


7.8573 


528.45 


147.3 


8.6 


33 


164.26 


867.27 


6.0880 


860.33 


190.1 


7.5 


33 


207.08 


1093.4 


4.8290 


1367.3 


239.6 


6.3 


31 


261.23 


1379.3 


3.8281 


2175.5 


302.3 


5.5 


35 


329.35 


1738.9 


3.0363 


3458.5 


381.3 


4.7 


36 


415.24 


2192.5 


2.4082 


5497.4 


480.7 


4.3 


37 


523.76 


2765.5 


1.9093 


87421 


606.1 


4.0 


38 


660.37 


3486.7 


1.5143 


13772. 


764.3 


3.7 


39 


832.48 


4395.5 


1.2012 


21896. 


963.6 


3.6 


40 


1049.7 


5542.1 


.9527 


34823. 


1215. 


3.0 



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a> 



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rH C<1 03 CO T*< 



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1-1 C<I C<1 CO '^ 



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14 



Consulting this table to see how the resistance of .395 
was found for the two 500 feet leads or mains, look down 
the left hand column until we come to No. 6. The second 
column shows that the diameter of No. 6 wire is .162 mills, 
or 162-1000 of an inch. In the first section of the table 
we see that 1000 feet of No. 6 wire has a resistance of .395 
ohms. 

Fig-. 5 shows the ordinary lighting circuit with the 
dynamo in the middle of the circuit and the lamps about 
equally distributed along the circuit. 



lAmP iTAmp. ^ 2^/^Atnp 




2SA7 



^^^^r M 



9 Amp. 



60 Ft 



8Lt3. 26Us 



13 Ft 



•00 n 



10 Lta. 



10 ft 



sort 



22L%5. l6Lt». 



Figure 5 
Ordinary lighting circuit. 



Theoretically at every branch the size of the mains 
should be reduced, but, as this is practically impossible, it 
is usual to carry the large wire far enough and make a 
reduction in size only once or twice. In Fig. 5 we will 
allow a loss of two volts in the leads. Taking the left hand 
side of the circuit, if we assume the full amount of 241/3 
amperes to be carried, 75 feet plus 60 feet, or 135 feet, we 
shall get a wire large enough and the drop will be less 
than the two volts rather than more. This will allow for 
some additional drop in the additional 40 feet for the last 



15 

circuit. We have then two volts equals 241/2 multiplied by 

2 
ohms, or ohms equals equals .0816 ohms. We must 

X. 



^2 
find a w^ire then that has a resistance of .0816 ohms in 270 

1000 
feet. Such a wire will have a resistance of multi- 

270 
plied by .0816 for 1,000 feet, or .302 ohms per 1,000 feet. 
Consulting the table, we find that No. 5 wire has a resist- 
ance of .313 per 1,000 feet, and we will select this as the 
size to be used. On the right hand side of the circuit we 
will select a wire large enough to give two volts drop if all 
the current is carried to the second branch circuit, or 2 

2 
eqvals 25 multiplied b}^ R, or E equals — equals .OS 

25 
ohms. As the length of the wire is 170 multiplied by 2 

equals 340 feet, the resistance of 1,000 feet of this wire will 

1000 
be multiplied by .08125, or .235 ohms. 

340 

Consulting the table we see that No. 4 wire has a re- 
sistance of .248 per 1,000 feet, and we willsselect this. For 
short branch wires it is best to use the table of the fire 
underwriters, which limits the amount of current a wire 
shall carry by the heating of the wire. Taible II shows 
these values. 



16 

Currents allowed by fire underwriters in wires of various 
sizes: 

TABLE II. 
Table A. Table B. 

Rubber Covered Wires. Weatherproof Wires. 

B. & S. G. Amperes. Amperes. 

18 3 5 

16 6 8 

14 12 16 

12 17 23 

10 24 32 

8 33 40 

6 46 65 

5 54 77 

4 05 92 

3 76 110 

2 90 131 

1 107 , 156 

127 185 

00 150 220 

000 177 262 

0000 210 312 

For small isolated plants 5 volts drop is usually allowed 
so that the sizes for the leads we have figured for 2 volts 
drop are plenty large enough for good results for such 
plants. The drop is often expressed in per cent. A 5 per 
cent, drop is 5 per cent, of 110 volts, or nVo volts. 



T 



Figure 6 Figure 7 

Drop in branch circuit Drop in same circuit connected 

tapped at end. in center. 



17 

If possible, branch circuits should be tapped on to tlie 
mains at the center of the branch, in order to secure a 
more even voltag-e at the lamps. 

If the branch wires in Figs. 6 and 7 are both of the 
same size, it is easy to see that the drop in the branch wire 
as connected in Fig-. 6 is very much greater than in Fig. 7. 
In fact, the drop in Fig. 7 is only one-fourth of that in 
Fig. 6, for in Fig. 7 each branch carries half the current 
half the distance that it does in Fig. 6. Sometimes when 
from circumstances the drop in the branch circuits is bound 
to be very great, it is possible to connect them so that 
while there is a great deal of drop in each line all the lamps 
receive the same voltage. 



66666666666666666"^ 



Figure 8 

Method of connecting lamps so as to get even voltage at lamps 
even with great drop in the line. 

Fig. 8 shows such a connection. If the drop in each 
wire were five volts from one end to the other and the mains 
supplied 115 volts, each lamp would still get 110 volts. The 
great trou'ble with such schemes is that, although they 
work well when fully loaded, when partly loaded the volt- 
age on the lamps that do burn is excessive and certain to 
shorten the life of the lamps. The only way to install a 
plant that will be perfectly satisfactory in the way of drop 
in the lines is to use wire large enough, so that when fully 
loaded the drop is small, then with light loads it will be 
still less. 



18 

CALCULATION OF FEEDERS FOR STREET RAILWAY 

WORK. 

In street railway wiring we have the peculiar case that 
only one side of the line is wire and the earth is used for 
the return. 



FCEDER 
TROLLEY 





Figure 9 
Electric circuit of street car system. 

The rails are electrically connected to each other by 
bonding*, and also are connected to the dynamo at the 
power house. It is usual to connect the dynamo to the gas 
and water pipes in the city, so as to take the current that 
naturally flows in them. In a well-bonded track there is 
not much loss of voltage in the return or ground circuit, 
and all the loss is figured in the overhead wire. The trol- 
ley wire is usually No. 1 or No. 0, so as to give mechanical 
strength. The trolley ware is supplied from feeders, w^hich 
are large wdres running from the dynamos and connected to 
the trolley wires at various points. For the heaviest loads 
at least 10 per cent, loss or 50 volts is allowed in the feeder. 
How large should a feeder three miles long be to carry 300 

50 

amperes with 50 volts loss? Here we have equals 

300 



19 



ohms in feeder equals — . As there are three miles of feed- 

6 1 1 

er the resistance per mile will be — multiplied by — 
1 6 3 

equals — , or .0555 ohms per mile. The table does 

is' 

not give the size of a wire so large as this, but it 
table does not give the size of a wire so large as this, but it 
will be ten times as large as one that has ten-eighteenths, 
or .555, ohms per mile, or a wire a little less than ten 
times as large as IS'o. wire, is what we want. This will 
be a wire of about 105600x10 circular mils, or about 1,000,000 
circular mils, or about one inch in diameter. Such a wire 
is very expensive to put up, so that it would be cheaper to 
install four wires ^^ inch in diameter, as these would have 
the same size and carrying capacity as the single large wire. 

The calculations required in wiring are almost univer- 
sally used in connection with constant potential circuits, 
cuits. 

There are two ways in wliich electricity is distributed: 
First, constant potential; and second, constant current. In- 




rrnrrnSn 



Figure 10 
Are light circuit. 



20 

candescent lighting and a great deal of arc lighting, street 
railway systems and all important plants for the transmis- 
sion of power are operated on the constant potential sys- 
tem. Most of the arc lights that are in use, especially the 
older ones, are operated under the series system. In the 
first case, each lamp or motor receives the full voltage of 
the system and only part of the current. In the second, 
each lamp receives the full current flowing in the system, 
but only part of the voltage. Each arc lamp m a series 
system takes from 50 to 55 vplts. 

Some of the latest arc dynamos will carry 125 or even 
150 such lani]3S, which requires a pressure of nearly 8,000 
volts. Such a voltage is very dangerous, and this is one 
reason why the series system is not in general use. A 2,000 
candle power arc lamp requires 9 to 10 amperes, and a 1,200 
candle power from 6 to 6^2. No. 6 B. & S. is usually used 
for 2,000 candle power arc light lines and No. 8 for 1,200 
candle power. A convenient rule b}^ which to calculate the 
resistance of copper wire in the absence of a table is R 
equals 10.8 multiplied by length in feet divided by diameter 
in mils, or one-thousandth of an inch squared, or 

10.8 multiplied by L 
R equals ■ 



in which L equals length in feet and M equals the diameter 
in mils. 



21 



QUESTIONS ON WIRING. 

1. What is known of the nature of electricity? 

2. What is known of the laws governing* its action? 

3. What analogy may be used to illustrate the action 
of electricity? 

4. In the analogy of the action of water and electric- 
ity, what corresponds to electric pressure? What to elec- 
tric current? What to electric resistance? 

5. What is the unit of electric pressure? 

6. To what unit in hydraulic work does it correspond? 
7.^ What is the unit of electric current? 

8. What is the unit of electric resistance? 

9. What is Ohms Law? 

10. Is Ohms Law peculiar to electricity or does the 
same general law hold in other work? Give an example. 

11. How many volts does an ordinary storage battery 
produce? 

12. What pressure is usually employed for incan- 
descent lamps? 

13. How many amperes are used by an ordinary incan- 
descent lamp? How many by an arc light? 

14. What is the resistance of 1,000 feet of. copper wire 
1-10 inch in diameter? 

15. Give an example different from that in the 
text of the loss of pressure with the transmission of fluids. 



22 

16. On what does the loss of pressure in a pipe carry- 
ing a fluid depend? 

17. To what does the pump in a system for distribut- 
ing fluids correspond in an electric system? 

18. Give other points of analogy between the example 
you have selected and the electric system. 

19. Upon what does the loss of pressure in a wire de- 
pend? 

20. Draw a diagram of a constant potential electric 
system with four branch circuits and 38 lamps distributed 
among them. 

21. What part of the whole resistance of a circuit 
should the lamps be? 

22. What is "drop"? 

23. What is the ideal condition as regards drop in wir- 
ing up an electrical plant? 

24. Why is it not possible to realize the ideal condition? 

25. What are calculations in wiring required for? 

26. What are the three different statements or forms 
of Ohm*s law? 

27. Which is the most important in wiring problems? 

28. Write out in your own words what equation (2) 
means. 

29. How many volts are lost in a circuit carrying 120 
amperes and having a resistance of 1-30 of an ohm? 

30. What sized wire would be required for such a cir- 
cuit if it were 400 feet long? 

1 

31. How many amperes are flowing in a wire of — 

25 
ohm if there is a drop of two volts in it? 



23 

32. What is the resistance of a -wire that has 3% volts 
drop when carrying 45 amperes? 

33. If a dynamo supplies current to its circuit at 114 
volts and each main wire has a drop of three volts, what 
voltage is there on the lamps? 

34. A certain station fed a number of lamps at a con- 
siderable distance. The drop was 55 volts, the resistance 

1 

of the circuit was of an ohm. How many amperes was 

220 
the station carrying? 

35. What drop is allowed in the mains of the best 
plants? 

36. A dynamo in a basement is used to light a buildings 
The wires are carried 100 feet before any branch circuits 
are taken off, and then one is taken off every 12 feet for 96 
feet. What sized wire would be required to carry 400 am- 
peres with a drop in the wires of three volts? 

37. Why is it best to attach a branch circuit to the 
main in the middle? 

38. A certain plant is used to light a building. It is 
desired to light another building 800 feet away and using 
1,000 lamps. In order to save copper, 115 volt lamps are 
used in the first building and 100 volt lamps in the second 
building. At 15 cents per pound, how much less would the 
copper for the mains cost with 100 volt lamps in the second 
building than with 110 volt lamps? 

39. What are the objections to such a scheme as out- 
lined in question 38? 

40. In branch circuits carrying a large number of 
lamps, what table should be employed to determine the size 
of the wire? 



24 

41. Haw many volts drop are usually allowed in the 
feed wires of street railway circuits? 

42. How do the currents return from the street cars 
to the dynamo? 

43. Why does such a return as is used in street 
railway work save copper? 

44. How large a wire would be required to carry 500 
amperes l^^ miles with a drop of 75 volts? 

45. What would such a wire cost at .14i^ per pound? 

46. If 125 volts drop wer(* used, what current would 
this wire carry? 

47. If 500 amperes were carried on a wire at 125 volts 
loss IVo miles, how much would the wire cost at .14^2 per 
pound? 

48. AYhat size of trolley wire is usually employed in 
street railway work? 

49. Sketch out a system of wiring for street railway 
circuit by which the voltage when near the power house is 
less than when at a distance from it. 

50. In what two ways is electricity distributed? 

51. For what is the series system used? 

52. ^Vhat is the characteristic feature of the constant 
potential system? 

53. Of the series system? 

54. What current is required for a 2,000 c. p. arc lamp? 

55. What current is required for a 1,200 c. p. arc lamp? 

56. \Miat is a convenient rule for calculating the re- 
sistance of a copper wire in the absence of tables? 



CHAPTER II. 

ELECTRIC BATTERIES. 

In the year 1786 Galvani was making some experiments 
with frogs' legs and had a number supported by the spinal 
cord from copper hoops attached to an iron railing. He 
noticed that when the muscles touched the railing that the 
frog's legs contracted spasmodically. This experiment led 
finally- to the production of the electric batter^'. 

Volta, in the year 1800, produced the so-called voltaic 
pile, which is one of the simpler forms of a battery. The 
easiest and most simple way to make a battery is to insert 
in a jar partially filled with acidulated water, or even brine, 
a strip of zinc and one of copper. Upon joining the zinc 
and copper outside the solution by a metallic conductor, a 
current of electricity will flow from the copper to the zinc 
through the conductor and from the zinc to the copper 
through the acid. The way in which the current flows 
through the acid is not thoroughly understood, but this 
flow is accompanied by the oxidation or slow 15tirning of the 
zinc and by the evolution of hydrogen gas on the copper. 
The primary cause of the flow of the current is the com- 
bustion or oxidation of the zinc, and if the conditions are 
properly arranged the amount of current that flows is 
strictly proportional to the amount of zinc consumed. 

The appearance of the hydrogen gas on the copper re- 
duces the current which flows by covering it to a great ex- 
tent with a thin layer or coating of hydrogen gas. The 
battery will deliver much more current when means are 
provided to prevent the formation of gas upon the copper. 



26 

table iii. 
electko-cht!:mical series of the elements. 



— 


+ 


Oxygen 


Caesium 


Sulphur 


Potassium 


Xitrog-en 


Sodium 


Flourine 


Zinc 


Chlorine 


Iron 


Bromine 


Copper 


Iodine 


Silver 


Phosphorus 


Mercury 


Carbon 


Platinum 


Antimony 


Gk)ld 


Hydrogei 


a 



The process of coating- the copper with hj^rogen gas 
is called polarization. The zinc plate is called the positive 
element, the copper plate is called the negative element. 
The binding post by which the current leaves the copper 
:s called the positive pole, because the current flows from 
this binding post through the outside circuit to the nega- 
tive pole on the zinc plate. Some metals may be used in 
place of the zinc as the positive element in the battery; 
among these the more important are potassium and sodium. 
Many metals may be used to take the place of copper, but 
the material most fret^uently employed is carbon. 

A battery composed of zinc arid carbon has a much 
higher electro-motive force than one'in which the zinc and 
copper are used; in fact, the elements may be arranged in a 
series in which any one may bo lised as a positive element 



27 

in combination with any below it, and as a negative ele- 
ment when used in combination with any above it. Table 
No. 3 is such a list. 

Zinc and copper in a solution of sulphuric acid give an 
elctro-motive force of about one volt. Zinc and carbon 
give about two volts. Zinc and carbon with an alkaline 
solution, such as salamoniac or potash, give about one volt 
and one half. Various means are employed to prevent the 
hydrogen from appearing or adhering to the negative ele- 
ment. Some of these are mechanical, such as the use of 
very fine metallic powder, such as platinum sponge, which 
permits the bubbles of gas to escape when very small, or 
by the use of a stream of air bubbles which mechanically 
carries away the hydrogen from the surface of the negative 
element. The first method is used in the Smee battery, in 
which the negative element i^; a thin plate of silver on 
which has been deposited a coatitig of very finely divided 
metallic platinum called platinum sponge. 

By all means the more important method for preventing 
the appearance of hydrogen on the negative element is the 
use of some chemical which consumes the hydrogen before 
it reaches the negative element. This is usually accom- 
plished by inserting the negative element in a porous cup 
w^hich is filled with a powerful acid or with some other ma- 
terial which burns up the hydrogen. 

When the zinc of a battery is consumed it combines 
with oxygen from the solution in which it is placed, and for 
every atom of oxygen which chemically unites with the 
zinc two atoms of hydrogen are evolved, and these travel 
from the surface of the zinc through the solution in some 
way toward the negative plate. If somewhere between 



28 

the positive and negative plates a porous cup is placed, the 
hydrogen will pass through the pores of this cup on its way 
toward the negative plate. 

If within the porous cup is placed a very powerful acid, 
the hydrogen is consumed or burned up as soon as it reaches 
this acid, and thus the polarization which would otherwise 
occur from the appearance of hydrogen gas on the negative 
plate is prevented. 

Zinc is used as the positive element in almost every 
battery. 

The reason wh}' primary batteries are not used for the 
purpose of developing power is not that they could not be 
so used, but because the zinc and sulphuric acid which 
would be required t/) produce the power are so expensive as 
to be prohibitive. Efforts are being constantly made to 
produce a battery in which carbon may be used as the posi- 
tive element. If such a battery could be commercially pro- 
duced with an efficiency equal to the zinc battery, it would 
revolutionize the present methods of producing power and 
be one of the greatest inventions. 

If a plate of carbon be immersed in fused nitrate of soda 
and an iron plate be used as the negative element, current 
will be obtained. There is a dispute as to the source of 
this current, some claiming that it is electro-chemical and 
others that it is produced by electro-thermal effects. In 
either case the battery has not been sufficiently effective 
to be practical. 

A very powerful battery for experimental purposes (see 
Fig. 11) may be constructed by using a number of carbon 
brushes or plates fastened parallel to and close to each side 



29 



of the zinc plates and arranged so as to be plunged into a 
solution of sulphuric acid, water and bi-chromate of pot- 
ash. 




Figure 11 
Dip or plunge battery. 



This solution may be made by adding to one quart of 
water one-half pint of commercial sulphuric acid and one- 
quarter pound of bi-chromate of potash. 

The writer has obtained a current of 30 amperes from 
a single cell of this battery, six inches in diameter and six 
inches deep. It is necessary to provide means by which 
the plates maj'- be raised from the solution as soon as the 
occasion for their use is past. 

In order to get the best results from the use of the zinc 
plate when made of commercial zinc, it is necessary to 
amalgamate it or wet the surface with liquid mercury. 
This may be easily done by first mechanically cleaning the 
plate, next removing any grease by the use of potash or 



80 



soda, and third by immersing it for a few moments in an 
acid. The acid which is intended to be used as an electro- 
lite for the battery will answer. This will cause the zinc 
plate to present a perfectly clean surface, and the mercury 
will quickly spread all over it. This treatment prevents the 
acid from attacking the zinc when the outside circuit is not 
closed. 

Below^ is a table giving the names of a num'ber of the 
more prominent cells in use, and the voltage on an 
open circuit, the electrolite used and the character of the 
plates. 

TABLE IV. 
DATA OF COMMON BATTERIES. 



Name of CelL 


E.M.F. 


Plates. 


Electrolite. 


Bunsen 

Groove 


1.95 
1.93 
1.07 

1.47 

1.50 

.90 

2.00 


Zinc 

a 

n 

a 
n 

Load 


Carbon 

Copper 

Carbon 

Copper Oxide 
Lead 


(■ Nitric and 
( Sulphuric Acid 
/ Nitric and 
t Sulphuric Acid 
f Copper Sulphate 
\ Zinc Sulphate 

Salamoniac 


Gravity 

Leclanche 


Dry Cell 

Edison Lelande 

Lead Storage 


Salamoniac Paste 
Caustic Potash 
Sulphuric Acid 



It is a fact that with perfectly pure zinc and all condi- 
tions being perfect, the passage of a certain amount of 
current through a battery is invariably accompanied by the 
solution or consumption of a certain amount of zinc. 

Conversely, if a current from an outside source be passed 
through a battery from the zinc through the 



31 

electrolite to the carbon, metallic zinc will be deposited 
from the solution, provided the battery has been used 
before the experiment is made. 

In fact, the amount of electricity which passes through 
a properly arranged solution may be very accurately meas- 
ured by the amount of metal which is deposited from the 
solution. An instrument arranged to measure current in 
this way is called a volta-meter. 

Practical electricians will recall the old Edison meters, 
by which current was measured and sold to customers from 
the old Edison stations. 

In this instrument the current was caused to pass from 
one plate of zinc through a solution of sulphate of zinc 
and out through a second plate of zinc. The passage of ten 
amperes for ten hours through this meter causes the solu- 
tion of 4.33 ounces of zinc from the first plate by which the 
current enters the solution, and the deposit of an exactly 
equal amount from the solution upon the second plate. 
Every month these two plates were removed and weighed 
and the weight compared with what it was a month before. 
The amount of current that had passed was calculated 
from the change in weight. The plate by 
which the current enters the solution is called 
the anode, and the plate by which the current leaves 
the solution is called the cathode. It will 'be convenient to 
remember that the current always carries the metal with it 
from the anode into the solution and from the solution on 
to the cathode. In fact, it is easy to determine the direction 
in which a current is flowing by causing all or a part of 
the current to pass through a glass tumbler partly filled 
with a solution of sulphate of copper or blue vitriol, in 



32 

which are immersed a couple of nails, one connected with 
each side of the circuit which is to be tested. On one of 
the nails will appear bubbles of gas, while the other will be 
more or less rapidly covered with a layer of metallic copper. 
The current will flow from the first nail through the solu- 
tion to the second nail. 

A very great deal of attention is now being given to the 
chemical changes that are brought about by the ac- 
tion of electric current upon the various chemical com- 
pounds, and it is the writer's belief that the greatest ad- 
vances in electrical knowledge during the next few years 
will be made along- this line. 



'to 



ELECTRO-PLATING. 

We have discussed above the principles upon which elec- 
tro-plating depend. 

The general scheme is to cover one metal with a thin 
layer of another metal by electro-chemical means. To do 
this a solution is prepared and in this solution are immersed 
a number of anodes, usually of nickel, silver, copper, gold or 
brass, with which it is desired tc plate the second metal. 
In the same solution is immersed the metal to be plated. 

A current is passed from the anode through the solu- 
tion to the metal to be plated, or cathode. The action of 
the current is to decompose the solution and deposit the 
metal from the solution on the cathode, ajt the same time 
forming a portion of acid which in some way passes through 
the solution to the anode and there dissolves just as much 
of the anode into the solution as was deposited by the cur- 
rent out of the solution. 



33 

The amount of metal deposited upon the cathode de- 
pends upn the amount of current which flows and upon 
the time it flows or upon the ampere houra ot current. If 
the amount of current is properly arranged, the metal will 
be deposited from the solution in an even adhesive layer. 
If too much current flows, the metal will not be deposited 
in such a firm layer and the corners will have a blackened 
appearance, when the work is said to be burned. The skill 
of the plater comes, first, in getting the work to be plated 
chemicall^^ clean; second, in arranging the solutions prop- 
erly; third, in adjusting the lamount of current to the so- 
lution and the amount of work. One kind of solution is 
used with zinc, another with nickel, another with silver, 
and another with copper. 

Each solution requires special treatment, and to get 
good results, expert knowledge. 

It is a peculiar fact that a mixture of metals, such as 
brass, may be used in plating, but that the voltage required 
with such a solution is two or three times higher than that 
required by copper or nickel. 

Below will be found a table of the elements, giving their 
names, atomic weights, relative resistances by volume, rela- 
tive resistance by weight and weight deposited by ten am- 
peres in ten hours. 



34 



TABLE V. 



PROPERTIES OF METALS 







X 


a; 










t -c 






'C 




• >> 




*^ 


i>. 




> 
o 


'6 ^ 


i2 3 




nds D(ipos 
en hours b 
Amperes 














c; 


t:^^u 


2^ 


B 




8.94 
10.5 
19.26 
2.56 
7.13 
21.5 
7.84 
8.82 
7.30 
11.4 
8.5 
6.72 


1^ '\^ ^ > 


2 




Copper 


1.00 
1.113 
2.203 
.526 
2.732 
13.62 
5.33 
7.69 
6.75 
15.55 
12.16 
16.69 


1.06 

1.00 

1.27 

1.95 

3.74 

6.02 

6.46 

828 

8.78 

13.05 

13.92 

23.60 


63.4 
108. 
197. 

27. 

65.2 
197. 

56. 

58.8 
118. 
207. 

122. 


.2636 


Silver 


.8980 


Gold 


.5160 


Aluminum 


.0569 


Zinc 


.2710 


Platinum 


.4145 


Iron 


.0776 


Nickel 


.1222 


Tin 


.2t5:3 


Lead 


.4303 


German Silver 




Antimony 


.1863 


Manganese Steel 


7.8 
13.6 


34.82 
89.76 


42.43 
62.73 


200 




Mercury 


.8^.15 


Bismuth 


9.8 


89.92 


87.23 


210. 


.:i492 



35 

STORAGE BATTERIES. 

When two plates of lead are immersed in a solution of 
sulphuric acid and a current is passed through the cell, 
there is a tendency to produce an oxide of lead on one plate 
and spongy or metallic lead on the other plate. If the 
plates are properly prepared and the current is sent 
through the battery repeatedl3% first in one direction and 
then in the other, the cell will finally be completed or 
formed. This method of making a storage cell is called 
the Platite process. 

In a completed storage battery, passing the current 
through the battery is called charging it, and the charging 
produces chemical changes on the plates, which will pro- 
duce electric currents if the plates are connected by a wire 
outside the battery. 

When current is flowing from the battery it is said to 
be discharging. The batter3^ ^i^l continue to discharge un- 
til the chemical products formed by the charging current 
have been reduced to their original state. The advantages 
possessed by the storage battery over the primary battery 
are that there is no polarization and the resistance of the 
battery may be made very much lower than that of a pri- 
mary battery. 

As its name indicates, the storage battery is practically 
a device for absorbing energy from an electric circuit at 
one time and restoring it to the electric circuit at some 
subsequent time. The charging current in a good battery 
may vary between wide limits, but the best results will be 
obtained from a moderately small amount of charging cur- 
rent. The same thingr is true of the amount of the current 



36 



during" discharge. The best modern storag-e batteries used 
for horseless carriage worlv, where extreme lightness is es- 
sential, have a capacity of two ampere hours per battery 
tor every pound of w^eight in the battery and a capacity of 
four watt hours per pound in the battery. 

The two principal uses for storage batteries at the pres- 
ent time are for storing power in central stations during 
times of light load, so that it can deliver the powder during 
the time of the heaviest load, and second, for furnishing 
electric current for motors for'horseless carriages and elec- 
tric launches. Storage batteries may also be used to great 
advantage near the end of a long line which has an inter- 
mittent load on it. The batter}^ will absorb current during 
times of light load and deliver it during times of heavy load, 
thus making the current that comes over the line from the 
central station practical!}' constant. The great objections 
to the storage battery are its cost and weight. So far, no 
one has succeeded in making a practical battery out of any 
other material than lead. 



QUESTIONS ON CHAPTER II. 



BATTERIES. 



1. What two men were chiefly instrumental in the early 
development of the electric battery? 

2. Describe a way in which a simple battery may be 
constructed. 

3. In which way does the current from a battery flow 
in the outside circuit? 

4. What is the real cause of the flow of current in a 
battery ? 

5. What is polarization? 

6. What is the positive element in a battery? What is 
the negative element? 

7. iWhat is the positive pole of a battery? 

8. What metals may be used to advantage in place of 
copper in a battery? 

9. Consulting table No. 2, why is it that zinc and car- 
bon produce a higher E. M. F. than zinc and copper? 

10. What means are used to prevent hydrogen from ap- 
pearing on the negative element? 



A 



38 

11. Describe a chemical means for preventing hydrogen 
from appearing on a negative element? 

12. Why are primary -batteries not used to develop 
power? 

13. Describe a battery in which carbon is used as a 
positive element. 

14. How may a powerful battery for experimental pur- 
poses be made? 

15. In order to get the best results from a zinc plate 
when used in a battery, how must it be treated? 

16. What is the relation between the amount of zinc 
consumed in a battery and the amount of current it pro- 
duces? 

17. What is a voltameter? 

18. Describe the Edison current recording meter. 

19. What is an anode? What is a cathode? 

20. Does a current of electricity carrj^ a metal with it 
or against it? 

21. How may the direction of a current be determined 
by chemical means? 



ELECTRO-PLATING. 

1. What is accomplished by electro-plating? 

2. Describe the process of electro-plating. 

n. On what does the amount of metal depositee' depend? 



39 

4. What is the effect of having- too much current in 
electro-plating? 

5. lb it possible to plate with an alloy, such as brass? 
If so, how? 



STOEAGE BATTERIES. 

1. What is a storage battery? 

2. Describe the process of charge and discharge. 

3. What advantages does the storage battery possess 
over ordinary batteries? 

4. For what are storage batteries used? 



CHAPTER ra. 



MAGNETISM. 



If a hard piece of steel be brought into contact with a 
magnet it will bocome magnetized and will retain more or 
less of the magnetism. If steel of the proper kind and 
which has had the proper treatment is chosen, the mag- 
netism will be constant, almost absolutely constant. Tung- 
sten steel, artificially aged, is used for volt meters and 
measuring instruments in which the accuracy of the instru- 
ment depends on the constancy of the magnetism of the 
steel, and the steel meets the requirements. If a magnet 
is supported so as to be free to turn in a horizontal plane, 
it will set itself north and south, as is seen in the mariner's 
compass. 

The pole that turns toward the north is called the 
north or N. pole and the other the south or S. pole. It is a 
fact that like poles repel each other and unlike poles at- 
tract each other. 

The earth on which we live is a great magnet, and this 
has its S. magnetic pole at or near the north geographical 
pole, for if by definition a N. pole is one that points to the 
north and unlike poles attract each other, the X. pole of the 
compass must point toward the S. magnetic pole of the 
earth. 



41 

A magnet is surrounded by what is called a iield of 
force. 

What are called lines of force are supposed to spring 
from the iron or steel at the north pole, pass through the 
air to the south pole, enter the iron and pass through it to 
the north pole. The lines of force are said to flow in the 
direction indicated. This should be carefully kept in mind, 
as it will be used a great deal later. 

A line of force is always 
a closed curve, and if any 

one travels alono- the whole 

of a line of force one will al- 
ways come to the starting 
point. A line of force is the 
direction of the magnetic 
force at any point 



'^ - - ' " 





The lines of force from "^X^li^-'S^lziirj-'Z^^^y"^^" 



the earth are flowing in the 



. "»-." --- ri_- ' 



air from the south to the ^ * *"-^r::". t- - ' 

north. Near the equator the Figure 13 

magnetic force acting on a Bar magnet and field of force. 

horizontal compass needle is 
greater than in other parts 
of the earth. 

The earth as a magnet acts on a horizontal compass in 
the United States with a force corresponding to from one 
to two magnetic lines per square inch. 

If a bar raagnet be placed under a piece of 
pasteboard or glass, and iron filings be sprinkled oyer the 
pasteboard or glass, they will arrange themselves along 



42 



the lines of force. A picture of the mag-netic lines produced 
in this wa3^ is called a magnetic spectrum. 

A bar mag-net bent into a TT shape is called a horse-shoe 
magnet, and it is interesting 'to get the mag*netic spectrum 
of such a magnet. (See Fig. 20.) The region of powerful 
influence is smaller than with a bar magnet, but much more 
intense. The spectrum of two horse-shoe magnets attract- 
ing* amd repelling- each other is very instructive. 

A ^vire carrj/ing a current has a 
very peculiar spectrum. This spec- 
trum consists of concentric circles, 
denser near the Avire than at a dis- 
tance form it, as indicated in the 
sketch. 

When the direction of the cur- 
rent is reversed, the direction of the 
lines is reversed. It is possible to find 
the direction of a current in a wire 
by the use of a compass by deter- 
mining in what direction the concentric mag- 
netic lines or magnetic whirl flows. A free north pole 
would move in the direction in which the magnetic lines 
flow, or would revolve around the wire. It is not possible, 
of course, to obtain a free north pole or a north pole with- 
out a south pole, so that all that can practically be discov- 
ered is the direction in which the north pole of a compass 
is moved. The direction in which the north pole is moved 
is the direction of the whirl, and the direction of the whirl 
bears the same relation to that of the current that 
the direction of rotation of a screw bears to its motion 
back and forth. 




Figure 14 

Magnetic spectum of wire 
carrying current. 




43 

If the north pole of a compass moves in a rig-ht hand 
direction, it shows that the lines of force flow right hand- 
ed and that the current is flowing away from the observer. 

If the north pole of a compass is moved to the right 
when placed over a wire 
carrying current, it 

shows that the whirl is right 

handed and the current is 

flowing away from the ob- 

; "^ '^ Figure 15 

server. Direction of current indicated by 

motion of compass needle 

If, on the other hand, placed under a wire 

■i. X XT • T,x X. carrying current, 

it moves to the right when ^ 

placed under the wire, it 

shows that the whirl is left handed and that current is trav- 
eling toward the observer. 

It is a fact that when current is caused 
to circulate around an iron or steel core, the core 
becomes magnetized, and if the current is strong enough 
the core becomes much more strongly magnetized than is 
possible with permanent magnets. It is easy to get a 
magnet of such strength that the armature is attracted with 
a force of 125 pounds per square inch, and in extreme cases 
the magnetism of a piece of soft iron has been pushed to 
such an extent as to produce a magnetic pressure of 1,000 
pounds per square inch. A piece of soft iron surrounded 
with such a circulating current becomes 'a powerful electro- 
magnet, but almost all the magnetism disappears when the 
current is withdrawn. 

There is a relation between the polarity of an electro- 
magnet and the direction in which the current circulates 
around the magnet core. When the current circulates 



44 




Figure 16 

Relation between polarity of 
electric magnet and direc- 
tion of exciting current. 



around the magnet in the direction of the motion of the 
hands of a watch, the pole facing 
the observer in a S. pole. 

A little thought will show 
that the magnetism of an elec- 
tro-magnet ma}^ be regarded as 
the sum of the magnetic whirls of 
the wires surrounding the core. 
An inspection of Fig. 17 will 
show this. 

A helix is a coil of wire carrying a 
current; the name is usually applied 
l^f (©/ 1^^ @ \^))y only to a single long spiral of wire. 
.. "!: ._roi ^ piece of iron placed in a helix carr}^- 

ing current becomes an electro-magnet. 
A helix carr^^ing current has all the 
properties of an electro-magnet, but 
the magnetic properties are not so pow- 
erful. 



.^r-^r 



^0777 



>_*f5. 



Figure 17 
Sho-wing that the mag- 
netic lines of a helix or 
electromagnet are due to 
the addition of the mag- 
netic whirls of the wires 
carrying the exciting 
current. 



in an acid solution 
copper are connected with a helix. 
This helix will turn and point north 
and south in the same way a com- 
pass w^ould. It is attracted or re- 
pelled by a permanent magnet in 
the same wa}^ that a compass is. If 
there were two of them floating in 
the same vat they would arrange 
themselves end to end with N. and 
S. poles adjacent. 



Fig. 18 shows a zinc and copper 
plate attached to a cork and floating 
The zinc and 




Figure 18 

Floating helix and 

electromagnet. 



^ 



45 



If now a piece of soft iron be placed in the helix all 
the above actions become much stronger, but this is the 
only dilference. A piece of hard steel may be made into a 
permanent magnet by being inserted into a helix carrying 
current. A helix with a large number of turns is called a 
solenoid. 

A very important relation exists between a wire carry- 
ing a current and a magnetic field. A magnetic field is a 
space through which the mangetic lines travel. 




Figure 19 

Magnetic spectrum of a helix ; compare with spectrum 

of bar magnet. 



^7=^ 






Figure 20 

Wire carrying current in a magnetic field tending to move 

in or out of the magnet. 



>^ 



46 



Fig. 20 sliovvs a liorse-shoc magnet and in such a mag- 
net the most powerful field exists between the ends. Fig. 
20 also shows a wire placed in this field and at right angles 
to the 2)]ane of the magnet. If, now, current be sent 
through this wire, it wnll experience a mechanical force 
tending to move it sideways across the lines of force, either 
into or out of the magnet. 




Figure 21 



Fig. 21 shows a method by which a wire carrying a cur- 
rent and free to move may be arranged. This is a most 
important experiment, and, if possible, should be performed 
by every one interested in the study of electricity. The 
experiment shown in Fig. 21 is the fundamental experiment 
showing why it is that a motor will operate. By reversing 
the experiment shown in Fig. 21, and by causing the wire 
to move across the lines of force, it is possible to generate 
current in the wire. This is a fundamental experiment, for 
it shows in the simplest possible manner how mechanical 
power can be transformed into electrical power, or how a 
dynamo works. The relations that exist betw^een the direc- 



47 



tion of motion of the wire, the direction of lines of force 
and the direction of the current in the wire when moved by 
hand or by mechanical force, is most easily remembered 
bv extending- the thumb, first and second finger of 




Figure 22 
Rotation of direction of lines, motion and current illustrated. 



the right hand at right angles to each other. When so ex- 
tended the thumb points in the direction of the motion, the 
first finger points in the direction of the magnetic lines, and 
the second finger in the direction of the resulting current. 
The rule for remembering the direction of motion, lines 
and current when the wire is supplied with a current from 



18 



a batter^' or other source is the same as the ease of a wire 
moved by mechanical rDrce, given above, except that the 
thumb, first and second lingers of the left hand are used 
instead of the right. 



D/RECTfON OF 




Figure 23 
Production of E. M. F. by moving wire in magnetic field. 




Figure 24 

Passage of current tlirough a loop in a motor 
and resulting motion. 

Fig. 24 shows an electric motor in which the rules 
given above may be applied. In Fig. 24 the N. pole is 
shown at the top and consequently the magnetic lines flow 
downwards, across the upper air gap and through the ar- 



49 



mature iron and across the lower air gap. if, now, cur- 
rent flows from some external source through the loop 
fr');a A to B, the wire in the upper gap will be forced to 
the left. 

As the current in the other side of the loop will be flow- 
ing in the opposite direction to that in the upper side, this 
part of the loop will be forced to the right; thus the wire 
in tlie upper air gap and the wire in the lower gap both 
tend to rotate in a direction opposite to that of the hands 
of a watch. Since the direction of the current in all the 
wires in the upper air gap in an actual armature is the same, 
each of these wires will be forced to the left and in a similar 
manner each of the wires in the lower air gap will be forced 
to the right. The sum of the mechanical forces acting on 
the wires in the upper and lower air gaps is the torque or 
twisting effort of the armature. The mechanical force de- 
pends on two things, viz: the number of magnetic lines flow- 
ing across the air gap and the current flowing in each wire. 
When a wire one foot long is in a field of an intensity of 
100,000 lines per square inch, there will be a mechanical 
force of .106 pounds or 1.7 ounces pushing the wire sideways 
for every ampere of current flowing in the wire. It is clear 
now why it is so necessary to fasten the wires to the arma- 
ture bj^ bands, for it is not the iron which tends to move, 
but the wire on the outside of the iron, and in order to 
communicate the torque from the wire to the iron some 
such means are necessary. 

Fig. 25 shows the same machine as Fig. 24, except that 
the armature is driven in the opposite direction by me- 
chanical powder. We have the north pole at the top and 
the current tending to flow through the ware in the same 
direction as in Fig. 24. There will be a drag on each wire 



J 



50 

proportional to the number of lines ■vvhicli flow across the 
upper air g-ap through the arnnature and across the lower 
air gap, and also proportional to the current which is flow- 
ing in each wire. 




Figure 25 

Motion of a wire in a magnetic field and the 
resulting current. 

Since there is the same mechanical drag in each wire 
in the upper air gap and an equal mechanical drag in the 
opposite direction in each w^ire in the lower air gap, it re- 
quires a mechanical torque or twisting effort on the arma- 
ture to force the wires carrying the current through the 
air gaps. It sometimes happens that when very excessive 
currents pass through the wires on an armature the me- 
chanical drag is such that the wires slip over the surface 
of the iron, usually cutting through the insulation at some 
point and burning out the armature. This is one advantage 
of the modern tunnel wound armature, for its construction 
gives an almost perfect mechanical support to the armature 
wires. When a wire moves so as to cut 100,000,000 lines of 
force per second, there is produced in this wire an electro- 
motive force of one volt. It will pay the student to per- 
form the experiments illustrated in this chapter, as he can 
in this way gain a first-hand knowledge of the fundamental 
principles upon which the operation of motors ayd d^^namos 
depend which can be secured in no other way. 



QUESTIONS ON CHAPTER III, 



1. What happens if a hard piece of steel is brought 
contact with a magnet? 

2. What is a mariner's compass? 

3. What is the north pole? The south pole? 

4. What is a field of force? 

5. In what direction do magnetic lines flow? 

6. What is a magnetic spectrum? 

7. What is peculiar in the magnetic spectrum of a 
horse-shoe magnet? 

8. Describe the magnetic spectrum of a wire carrying 
a current. 

9. What is a magnetic whirl? 

10. What is the relation between the direction of flow 
of current in a wire and the direction of the magnetic whirl? 

11. If the current in a vertical wire moves the north 
pole of a compass to the right when the compass is held 
between the wire and the observer, in what direction does 
the current flow? 

12. A wire running north and south causes the north 
pole of a compass placed over it to be deflected toward the 
west; which way is the current flowing in the wire? 

13. A lineman wished to learn the direction ocf the 
current in a wire over his head and observed that the com- 



52 

pass needle when held over the wire face down was deflected 
toward the east, the wire running- north and south. In what 
direction does the current flow in the wire? 

14. What is an electro-magnet? 

15. What is the difiPerence between a permanent mag- 
net and an electro-magnet? 

16. What is the relation between the polarity of an elec- 
tro-magnet and the direction in which the current circu- 
lates around the iron core? 

17. Is there any relation between the polarit}^ of an 
electro-magnet and the magnetic whirls in the wires of 
which it !s composed? If so, what? 

18. What is a helix? What are its properties? 

19. What is fhe difference between a helix and an 
electro-magnet? 

20. When a wire carr^nng a current is placed in the 
field of a horse-shoe magnet, what occurs? 

21. Explain the action of the mechanism in Fig. 20 
when it operates as a motor. 

22. Explain its action when it operates as a dynamo. 

23. What is the relation between the direction of the 
motion, direction of the lines and the direction of the cur- 
rent w^hen the apparatus is used as a dynamo? 

24. What is the relation between the direction of the 
motion, the direction of the lines of force and the direction 
of the current when the apparatus is being used as a motor? 

25. Why will the armature in Fig. 21 reverse its direc- 
tion of motion if the north pole were placed at the bottom 
instead of at the top? 



53 

26. Why is it that both wires in the loop in Fig. 21 tend 
to rotate the armature in the same direction? 

27. We have seen that the earth is a great magnet, with 
its south magnetic pole near its north geographical pole. 
If a person is riding a bicycle toward the west, in what 
direction will the E. M. F. be generated in the vertical 
spokes in the moving wheel? 

28. If a current is traveling in a coil of wire that is free 
to move, and the coil turns so that its plane is east and 
west, in what direction will a current be flowing in this 
coil? 

29. Two men standing in an east and west line, 50 feet 
apart, raise a steel tape from the ground. In what direction 
does the current tend to flow along the steel tape? 

30. In an Edison motor the armature is revolving right- 
handed as seen by the observer. If the pole on the left is a 
north pole, in which direction does the current flow in the 
wires under the north pole? 

31. When a wire is in a field of 100,000 lines per square 
inch, what is the mechanical force acting on the wire per 
ampere per foot? 

32. How many magnetic lines must be cut per second 
to produce one volt? 

33. Is there any other reason for banding down arma- 
ture wires to the core except to prevent the action of centri- 
fugal force? 



CHAPTER IV. 



THE MAGNETIC CIRCUIT. 



De La Rives' floating battery (Fig. 18) showed that a 
helix carrying a current is a magnet. If the current is 
measured and the number of turns counted, it will be found 
that the strength of a given helix depends on the number 
of amperes of current that flow through it, and if a con- 
stant current is used the strength of the helix depends on 
the number of turns. 

Putting these two facts together, we see that the 
strength of any helix is proportional to the product of the 
number of turns times the number of amperes or the am- 
pere turns. The number of ampere turns is a measure of 
the magnetizing force. 'By producing the magnetic spec- 
trum of a helix (Fig. 19) it will be seen that all the lines 
traverse the center of the helix and return through the space 
outside of the helix. If the diameter of the helix is large, 
more lines will flow through it than if it is small. If it is 
short, more lines will flow through it, other things being 
equal, than if it is long. A careful consideration of these 
experiments will show that there is the same relation be- 
tween the number of lines of force and the magnetizing 
force or number of ampere turns and the magnetic resist- 
ance that there is between the current, voltage and resist- 
ance in the electric circuit. If we allow N to represent the 
number of lines of force produced, A T to represent the 



55 



number of ampere turns, and M K to represent the mag- 
netic resistance or reluctance, we have N equals A-T divid- 

A T 
ed by M R, or . It will be noticed at once that this is 

M R 

Ohm's law transferred to the mag-netic circuit. 

The magnetic resistance is proportional to the length of 
the magnetic circuit and is inversely proportional to the 

1 
area of MR equals — , where 1 is the length of the magnetic 
A 

circuit and A equals the area. Substituting this in the for- 
mula we have 

A 
N equals A-T multiplied by — 

1 

If A and L be expressed in inch measurements, we have 

A-T multiplied by A 

N equals (4) 

1 multiplied by .3132 

We will now see what effect the introduc- 
tion of iron into the helix wili have. Figs. 18 and 19 show 
that current flowing in a helix produces lines of force in 
the helix and causes it to become a weak magnet. If a 
piece of soft iron be inserted in the helix, the iron becomes 
very strongly magnetized. 

It can be shown that a great many more magnetic lines 
of force traverse the helix when it has the ircm inside than 
before. Therefore the iron offers an easier path for the 
magnetic lines than the air did because more lines flow 
under the same circumstances when the helix is filled with 
iron than when the iron is absent. Under some circum - 



56 

stances the iron will transmit or allow to pass 3,000 times 
as matny lines ats the air. 

The presence of the iron multiplies the number of mag- 
netic lines by offering an easier path for the flow of the 
lines. If it was not for this multiplying action of the iron, 
dynamo electric machinerj' would be impossible. That 
property of iron, in virtue of which it conducts magnetic 
lines, is called permeability. 

Now the permeability of iron is not constant. When 
2)nly a few lines are flowing 'in a piece of iron the perme- 
ability or multiplying power is greatest. If the iron is al- 
ready carrying a large number of lines the permeability 
will be small. 

The capacity of the iron for carrying lines may be com- 
pared to the capacity of a sponge for soaking up water. 

When the sponge has only a little water in it, it wiP 
readily absorb more, but whe.n the sponge has taken u^ 
nearly as much water as it will, or is saturated, it will ab- 
sorb more water only with reluctance. When iron is car- 
rying about as much magnetism or as many magnetic lines 
as it will, it is said to be saturated. The permeability of 
iron at various numbers of lines per square inch in the iron 
or at various degrees of saturation has been measured, and 
the results obtained are shown in the following table: 



^ 



57 



TABLE VL 



TABLE OF PEKMEABILITY 



WROUGHT IRON 


CAST IRON 


o 


4) tn r-i !<-l 


2 






Ph o.So 


•i-t 

•fH 

cn 
a- 

2 


d — o « 
K :3 c <i> 


30,000 
40.000 
50.000 
60,000 
65,000 
70.000 
75,000 
80 000 
85 000 


3,060 

2,780 

2.48S 

2,175 

1980 

1920 

1500 

1.260 

1.030 

830 

610 

420 

280 

175 

95 

60 

40 

30 

24 

18 


98 
14.4 
20.1 
28.0 
32.8 
40.7 
50 
63 5 
82.5 
108.0 
156. 
238. 
375. 
629. 
1210. 
2000. 
3125. 
4333. 
5626. 
7777. 


3 06 
4.72 
6.29 
8.76 
10,26 
12.7 
15.6 
19.8 
25.8 
33.8 
48 8 
74 5 
117. 
197. 
378. 
626. 
978. 
1356. 
1761. 
2434. 


25,000 
30.000 
35.000 
40,000 
45 000 
50,000 
60,000 
70.000 


833 
580 
390 
245 
135 
110 
66 
40 


30 
51.7 
89.7 

163. 

333. 

454. 

90y. 
1750. 


94 
10.2 
27.5 
51. 

104. 
142. 

284. 
548. 


90.000 
95,000 
100.000 
105,000 
110.000 
115.000 
120 000 
125,000 
130,000 
135,000 
140,000 





58 



Uooooi 



tooooo 



eoooo 




leoo 



B. H. Curve 

Curves showing the same relations graphically that the 

table gives numerically. 

This table was calculated by measuring" the number of 
magnetic lines flowing* through an iron ring surrounded 
by a certain number of turns of wire (see Fig. 27) and 
comparing this with the number that would flow through 
the air when a wire coil of the sanje size, carrying the same 
current, w-as tested in the air (see Fig. 26). 




Figure 26 
Coil of wire in air. 



59 

The number of lines flowing in the coil in Fig*. 26 may 
be calenlated hy Formnla 4, or measured by coil and gal- 
anometer as in Fig. 27. 

Fig. 27 shows the same coil as in Fig. 26, except that 
the coil is fi.Ued with iron instead of air. 

The number of lines flowing may be measured with a 
small coil and galvanometer. By passing the same currents 
through both coils in Figs. 26 and 27 and coniparing the 
number of magnetic lines produced, the permeability of 
the iron is found. 

If there are 100 turns in each coil, and one ampere is 
flowing through each coil, suppose current in coil in Fig. 
26 produces 100 lines and current in coil in Fig. 27 produces 
18^,000 lines, then the permeability of the iron is 185,000 
divided by 100 equals 1,850 at this stage of saturation. 




Figure 27 
Same coil as in Figure 26 with iron core. 

In the above table the first column represents the num- 
ber of lines of force which flow through the iron. The sec- 
ond column is the permeability or multiplying power of the 
iron. The third column is the number of magnetic lines 



60 

there would be in air. The fourth column is the ampere 
turns required to force the magnetic lines through one inch 
of iron at the given density. The first part of this table is 
devoted to ordinary wrought iron and may be used in a 
general way to represent the magnetic properties of char- 
coal and sheet iron, soft sheet steel and cast steel. 

The second part of this table represents the properties 
of ordinary cast iron. 

It must be carefully kept in mind that while these ta- 
bles give a general idea of the map-netic properties of iron, 
no two specimens of iron are exactly alike, and if it is de- 
sired to get an accurate knowledge of the magnetic quali- 
ties of any particular sample of iron, it is necessary to make 
a separate test for this sample and construct a table similar 
to table Xo. 5 for each sample. It will be noticed that in a 
general w^ay wrought iron conducts the magnetic lines 
about twice as w^ell as cast iron. 

When formula (5) is revised, so as to introduce the per- 

a.. t, K A X /Lt 

meability of the iron, it becomes N equals (5) 

1 X .3132 

in which fi represents the value of the permeability. 

We will now take an example and calculate the ampere 
turns required to force a given number of magnetic lines 
through the various parts of the magnetic circuit. We will 
select the Edison type of bi-polar dynamo for this calcula- 
tion. The easiest way to make this calculation is to find 
the number of ampere turns required in each part of the 
magnetic circuit and add together the numbers so found. 



61 



In this example we will find the number of ampere 
turns required in the yoke, which is of wrought iron, next 
that required in each magnet core, next that required in 
each pole piece, then that required in each air gap and last 
that required in the armature iron. 

In Fig. 28 the dimensions of the parts have been indi- 
cated and the approximate length of the average magnetic 
line is shown. Let us suppose that 4,500,000 magnetic lines 
flow through the magnetic circuit of this dynamo. This 
will cause 4,500,000 divided by 54, or 83333, to flow per 
sqvare inch through the yohe. Tlie following formula may 

Nxlx.3132 
be deduced from formula 4: A. t. equals (6), in 

A x |W 



^ 16 i. ; 




Figure 28 
Magnetic circuit of Edison bipolar dynamo. 



b2 

which N equals the total flow of magnetic lines in the part 
of the magnetic circuit considered, 1 equals length in inches 
of this part of the magnetic circuit, A equals area in square 
inches of this part of the magnetic circuit; // equals the 
permeability of this part of the magnetic circuit, with the 
particular value of N that may exist and the value of u must 
in each case be found from the table. Substituting these 
quantities in formula (6) we have for the yoke X equals 
4,500,000; 1 equals 22 inches; A, or the area 
of the cross section of the magnetic circuit 
in square inches, which' in this case equals 
6 multiplied by 9, or 54; and fi, or the permeability, equals 
1,107. This is found by consulting the table, in w^hich it is 
seen that the permeability of wrought iron equals 
1260 at 80,000 lines per square inch. That the permeability 
at 85,000 lines per square inch is 1030. The permeability 
of 83,333 lines will be approximately 2-3 the difference be- 
tween these tw^o permeabilities, or 1260 — 153 or 1107. 

4,500,000x22x.3132 

a. t. equals equals 520 

54x1107 

The a. t. required in the magnet core will be found by 
substituting for N, 4,500,000 as before, for 1 or length of 
this part of the magnetic circuit, 10 inches. 

For A, or the cross section of the magnetic circuit at 
this point, we have 50.26 square inches, which is the area of 
a circle 8 inches in diameter. 

To ascertain the value of /^ it is necessary to find out 
how many lines per square inch flow through the magnet 
core. In order to do this, divide 4,500,000 by 50.26, which 
gives 89,53^ lines per square inch. This is sufficiently close 



63 

to 90,000 lines to take the permeability of 90,000 lines from 
the table, and, substituting* 830 for the value of /t^, we have 

4,500,000xl0x.3132 

a. t. equials equals 338 

50.26x830 

Next we take up the number of a. t. required in the 
pole piece. This is of cast iron and the area of cross sec- 
tion is indicated in the sketch as being 12 inches x 12 inches, 
or 144 square inches. 

The flux per square inch is 4,500,000 divided by 144 
equals 31,?50. The ampere turns required in this part of 
the magnetic circuit would be 

4,500,000x9x.3132 

a. t. equals equals 166 

^ 144x532 

It must be kept in mind that the pole pieces are of cast 
iron and therefore the permeability is inuch lower than if 
tliey were of wrought iron. 

The ampere turns required in the air gap are 

4,500,000xlx.3132 

a. t. equals equals 10,213 

138x1 

The air gap in an actual dynamo is partly filled with 
copper wire and insulation, but this conducts magnetic lines 
no better than air. 

The area of the air gap is calculated on the assumption 
that the pole pieces embrace two-thirds of the circumfer- 
ence of the armature. As per the sketch, the pole piece is 
12 inches long and the average diameter of the air gap Is 



64 

11 inches, and the circumference of a circle 11 inches in 
diameter is 34.54 inches. One-third of this is 11.5 and the 
area of tlie air g-ap is 11.5x12 equals 138 square inches. 

It will be noticed that the numoer of ampere turns re- 
quired in the air gap is vastly greater than that required 
in an}' other part of the magnetic Circuit, and is a good 
example of how much better a conductor of magnetic lines 
iron is than air or any ordinary material. The ampere 
turns required in the armature iron are 

4,500,000x9x.3132 
a. t. equals equals 84 

72x2077 

In this part of the circuit the area of cross section 
of the magnetic circuit is taken as 6 multiplied by 12 inches 
equals 72 square inches, because the shaft is 4 inches in 
diameter, and for reasons that will appear later the lines 
cannot flow across the shaft w^hen the armature is in motion. 

There are two coils on the dynamo, one on each magnet 
core, and each of these two are of equal powder and each 
does half the work of driving the magnetic lines around 
the circuit. If we wish to find the numiber of ampere turns 
that each should supply, we must add together half those 
required for the yoke, all in one magnet core, all in one 
pole piece, all In one air gap, and half those in the armature 
iron. Gathering these results together, we have: 

Half a. t. required in yoke 260 

All a. t. required in magnet core 338 

All a. t. required in pole piece 166 

All a. t. required in one air gap 10,213 

Half a. t. required in armature iron.. 42 

Total a. t. required in half of mag- 
netic circuit 11,019 



65 



Each of the two coils will then be required to produce 
11,019 ampere turns in order to force 4,500,000 magnetic 
lines around the magnetic cirouit. 

The method of calculating the size of wire required in 
the coil to produce this number of ampere turns will be 
explained in one of the succeeding chapters. 

The Edison type of dynamo is an excellent example of 
the older style of dynamos that were built eight or ten 
years ago. The prevailing style for large machines at the 
present time has the multipolar field and ironclad armature. 

The ironclad armature is well adapted for all sizes of 
machines, while the multipolar construction is especially 
advantageous in machines of large output, but for machines 
of less than 10 H. P. is not so good as the bipolar construc- 
tion, as will be explained in the chapter on Hysteresis and 
Eddy Currents. 

Figs. 29 and 30 show diagrams of the two styles of ar- 
mature in the same field frame. 




Figure 29 
Smooth core armature. 



m 



The chief reason t'ha^t ironclad armatures have come 
into use is that by means of this device the magnetic re- 
sistance of the air gap is very much reduced. 

The practical effect of the introduotion of the ironclad 
armature is to make the carrying capacity of the iron of 
the magnetic circuit the limit of the flux through the cir- 
cuit. 

The resistance to the magnetic flux in the air gap of 
the ironclad armature is not mer one-flfth that in a smooth 
core armature of the same capacity. The ironclad arma- 
ture maj^ be run so that there is only enough room betv^reen 
the armature iron and the iron of the field frame to permit 
of mechanical rotatiou- 

It will be noticed that the wire on the ironclad arma- 
ture is buried in slots, cut in the armature. This protects 
them from mechanical injury, and, more important still, 




Figure 30 
Iron clad armature. 



^ 



67 



gives them perfect mechanical support, so that there is no 
tendency to slide or move from their places as there is in 
the smooth core armature. 

'Practically all of the magnetic flux that passes into the 
armature must get through the bottom of the iron teeth of 
the armature, and the area of this part of the magnetic cir- 
cuit determines the total flux that can be used. 

We will now calculate the ampere turns required in a 
bi-polar machine with an ironclad armature, and also the 
ampere turns required in a six-pole field with ironclad ar- 
mature. 




Figure 31 

Magnetic circuit of 5 H. P. bipolar machine with iron clad armature, 

and cast iron field frame. 



68 



r 



A^ 



Oi 



5^ 



The bipolar machine is shown in Fig-. 31 and the dimen- 
sions are those actually nsed in a 5 H. P. motor. 

It will be noticed that in this machine the yoke is in 
two parts and half of the flux flows through each part. 

The frame is so designed that the flux is most dense 
in the frame in the pole pieces. The sectional area 
of the pole pieces is shown in Fig. 3?. 
The area will bo 9x5y, or 49^/;, less what 
is cut off of the corners. .A circle 3 inches 
in diameter has an area of about 7 square 
inches, which is 2 square inches less than a 
surface 3 inches square, so that the area of 
the pole piece will be 49 Vo minus 2 equals 
47-/2 square inches. 

This machine has a flux of 2,100,000 

lines. At this flux the density in the pole Figure 32 

niece will be 2,100,000 divided by 47yo equals Calculation of 
' " Sectional 

44,210. area of i)ole piece. 

The average length of the magnetic line 
in each pole piece is 4 inches. 

The permeability of cast iron at 44,2U0 is 153. Substi- 
tuting in the formula No. (6) we have 



2,100,000x4x.3132 

a. t. equals equals 362 in each magnet core. 

47.5x153 



The flux in the yoke can all be calculated at the same time, 
for the density all through the yoke is the same, and 
consequently the value of the permeability or /^ is the same. 



69 



flux is 2,100,000 divided by (2%xl0x2) equals 2,100,000 divid- 
ed b}^ 52.5 equals 40,000. The permeability at 40,000 lines 
per square inch in cast iron is 245. Substituting* we have 



2,100,000xl2x.3132 



a. t. equals 



equals 613 



52.5x245 
in each half of the yoke. 

The area of the air gap is not the whole area of the pole 
face, for with an air gap 1-16 inch long* there is a bunch- 
ing of the lines to a greater or less extent, as shown in 
Fig. 33. 

It is important to calculate the area 
of the air gap carefully, for on thi's will 
depend the number of a. t. in the air 
gap, and this number is much greater 
than that for any other part of the 
circuit, and an error in this calculation 
will have a greater effect on the total 
result than in any other. 




Figure 33 

Bunchingof magnetic 
lines in air gap. 



There are 48 sloits in a disc 7^2 
inches in diameter and each slot is .230 
inches wide; the circumference of the 
disc is 23.55. Each slot and tooth 
take up 23.55 divided by 48 equals .491. 
This leaves the top of the tooth .491 — 

.230 equals .261 wide. The lines will spread from the top of 
the teeth to the iron pole piece. Each pole piece embraces 
or covers 16 teeth. Experience teacheis that it is safe to 
assume that the lines spread from the top of the teeth, so 
that the top of the tuft is equal in width to the top of the 
tooth plus twice the width of the air gap, but the average 



70 



width will be only half this. The averag-e width of the tuft 
will be .261 plus .062 equals .323. 

Since the length of the armature is 51/2 and there are 
48 teeth in the armature, we have 16 tufts of lines each 5^/^ 
inches long x .323 wide. The area of the air gap is then 
16x5. ox. 323 equals 28.4. Substituting we have 



2,100,000xlx.3132 
a. t. equals equals 1447 

28.4x16 

The magnetic lines are very much crowded in the arma- 
ture teeth, and the density changes at each point in the 
length of the teeth, so that theoretically a separate calcu- 
lation would have to be made for each part in the length of 
the tooth. A sufficiently close approximation, however, may 
be made by making two calculations, one for the ampere 
turns required for a length of y^j inch at the bottom of the 
teeth and the other for the rest of the tooth. 

It is first necessary to iind the area of the 'bottom of the 
teeth. 

The slots are % inch deep, .230 inches wide and round 
at the bottom. This being; so, the narrowest place in the 
tooth will be .750 minus .115 equals .635 from the outside of 
the disc, for there is a circle .230 in diameter at the bottom 
of the slot. 

The circumference of a circle whose periphery passes 
throug^h the narrowest part of the tooth is 

3.14ir)x[7.5— .6;;5x2] equals 3.1416x6.23 equals 19.57. 

1-48 of this circumference equals .408. 

.408— .230 equals .178 inches, which is the width of the 
tooth at its thinnest point. 



<1 



71 

The area of the tooth at the bottom is .178x5.5x16 equals 
15.66. 

The flux at the bottom of the teeth is 2,100,000 divided 
by 15.66 equals 134,100. 

The permeability at this flux is 30—4-5(30 — 24) equals 
25. Substituting 

2,100,000xlx.3132 

a. t. equals equals 210 

15.G6x8x2o 

As indicated above, the ampere turns in the rest of the 
tooth may be found in one calculation. The width of the 
teeth in the narrow-est place is .178 and in the widest place 

.261+.178 

is .261. The average width is then equals .219. 

2 
The average area of the teeth will be 

.219x5.5x16 equals 19.3 square inches. 
This area gives a flux of 2,100,000 divided by 19.3 equals 
100,000, and the permeaibility at this density is 280 — 4-5 
(280 — 175) equals 19G. Substituting we have 

2,100,000x5x.3132 

a. t. equals equals 108 

19.3x8x196 
The last calculation to make is ampere turns required 
for the armature iron. 

The area of iron carrying lines is 5yox[7i4 — (IVsi-lVi)] 
equals 4%x5i/< equals 26.1. 

The flux per square TnclT w^TtT he 2,100,000 divided by 
26.1 equals 80,460. 

The permeability at this density equals 1,237. 
The a. t. required for armature iron 

2,100,000x5x.3132 

a. t. equals equals 102 

26.1x1237 



72 

Collecting- our results we have: 



'ts 



A. t. required in each mag-net c^ore 362 

A. t. required in each half of yoke 613 

A. t. required in each air g-ap 1,447 

A. t. required in bottom of teeth on one side.. 210 

A. t. required in body of teeth on one side 108 

A. t. required in half armature iron 51 

A. t. required in half magnetic circuit 2,791 

We must then have two' coils each with a magnetizing 
power of 2,791 ampere turns, or one coil with a magnetizing 
power of twice this, in order to force 2,100,000 lines around 
the circuit. It will be noticed that the number of ampere 
turns required in the air gap is over one-half the total am- 
pere turns required. A little thought w^ll show also that a 
small decrease in the flux would decrease the magnetizing 
power very great!}', and, if it was necessary to force a little 
more flux through the circuit, a great deal more magnet- 
izing power would be required. This is because the iron 
in the motor just calculated is almost saturated, and in 
some parts of the circuit is saturated. A small decrease in 
the flux would very greatly increase the permeability and 
so decrease the magnetizing power required in these parts of 
the iron magnetic circuit. 

It wull be seen that it is not possible to obtain exact 
results in making these calculations, for the permeability 
of the actual iron may be more or less than that given in 
the table. 

It will usually be found that the table is a little high 
for wrought iron and cast steel and about right for good 
soft sheet steel. The writer has used samples of cast iron 



^ 



73 

that were better than those given in the table, and also 
some that were worse. It is easy to get cast iron as good 
as that shown in /the table. 

An equally close approximation to the ampere turns 
required in the iron part of a machine may be had by taking 
the ampere turns required for one inch of iron at a density 
given by the table. 

Use tihe density closest to the one required, and if any 
mistake is made, make the result too large ra-ther than too 
small. 

The ampere turns required in the magnetic circuit of 
the six-pole machine shown in Fig. 34 has been obtained in 
this way. 




Figure 34 
Magnetic circuit of a 100 K. W. Westinghouse dynamo. 



^^ 



'74 

These figures are taken from a Westing-house 100 K. VV. 
dynamo. 

In this machine we will make six calculations, for the 
pole pieces are made of thin pieces of sheet iron riveted 
together. This makes the pole piece wrought iron and the 
yoke cast iron, and thus requires two calculations for this 
part of the magnetic circuit. In these calculations the fol- 
lowing notation will be used: 

equals number lines ^ per square inch. 

1 equals average length of magnetic circuit in the part 
of machine under consideration. 

A equals cross sectional area. 

// equals permeability. 

a. t. equals ampere turns. 

For the laminated pole piece 

2,500,000 

O equals = equals 55,000 

61/2x7 

1 equals 7. 

A equals 453,-^ square inches. 

fi equals 2331. 

From table No. 6 it is found that it will take 7.53 a. t. 
at this value of // to force the lines through oue inch of the 
iron; therefore it will take 7x7.53 equals 53 a. t. to force the 
lines through the whole of 1. 

For the yoke which is of cast iron 

A equals 40 square inches. 

1 equals lOy^ inches. 



1 



75 



2,500,000 

O equals equals 31,250 

2x40 

a. t. T)er inch equals 14 6. 

Total a. t. equals 10.5x14.6 equals 153. 

For the air gap: 
I equals Vg inch. 
Width of top of tooth 

20x3.1416 

—.359 equals .539 

70 

Number of teeth under each pole 7.4. 

Average wid'th of air space between one tooth and jwle 
face equals .539-4-. 125 equals .664. 

A equals .664x7.4x7 equals 34.4. 

2,500,000 

O equals equals 72i680 

34.4 

More accurate results will be obtained by using formula 
(6) in calculating the a. t. in the air gap, for in this part of 
the magnetic circuit there is no value of /i to be inserted. 
Substituting in formula (6) the a. t. required for the air 
gap is found to be 

2,500,000xlx.313e 

a. t. equals equals 2845 

34.4x8 



76 

A. t. required in Vg inch at bottom of tooth. 

1 equals '/j inch. 

Dianieter of circle through the thinnest part of to#th 
equals 20 — 5-|-.359 equals 15.359 inches. 

Width of tooth here 

3.1416x15.359 
— ; .359 equals .330. 



70 
A equals .330x7.4x7 equals 17.1. 

2,500,000 

O equals equals 146,200. 

17.1 

146,200 lines per square inch is beyond the Mmdts of the 
table, but it will require about one-fifth more ampere turns 
per hich over 2,434 as the difference between the a. t. re- 
quired at 135,000 and 140,000, or 24344-[6-5(2434— 1761)] 
equals 3242. Hence 

A. t. equals 1/8x3242 equals 405. 

A. t. required in remainder of tooth: 

L equals 2.5— V3 equals 23/^. 

(.330-f-.539) 
A equals x (7.4x7) equals 22.5 square inches. 



2,500,000 

O equals equals 111.110, 

22.5 



77 

A. t. equals 2%x237 equals 563. 

A. t. required in rest of armature iron: 

If the shaft and spider are 10 inches in diameter, the 
area of armature iron carrying* lines equals 20 — (5-i-10)x7 
equals 5x7. 

A equals 5x7 equals 35. 

L equa'ls 3% in one-half of armature. 

2,500,000 

O equals equals 71,500. 

35 

A. t. equals 3%xl3.6 equals 47. 

Summarizing our results we have: 

A. t. in one pole piece 53 

A. t. in yoke 153 

A. t. in air g-ap 2,845 

A. t. in bottom of teeth 405 

A. t. in body of teeth 563 

A. t. in armature iron 47 

Total 4,066 

The coil on each pole piece wiill have to be capable of 
producing 4,066 ampere turns in order to force 2,500,000 
lines through each one of the six magnetic circuits. 



QUESTIONS ON CHAPTER IV. 



1. On wha«t docs the strength of a helix carrying" a cur- 
rent depend? 

2. Is there any relation between the number of mag- 
netic lines generated by a current in a helix, the magnetiz- 
ing power of the helix and the magnetic reluctance offered 
by the path which the lines take? If so, what? 

3. If the equation of a magnetic circuit be compared 
to Ohm's law what quantity in the magnetic circuit corre- 
sponds to the current? What corresponds to the voltage? 

4. To what is the magnetic resistance of a circuit pro- 
portional? 

5. What is the effect of the introduction of iron into 
a helix? 

6. Why is it that a number of magnetic lines traversing 
a circuit is increased more bj^ placing a piece of iron inside 
the helix than by filling the space around the outside of the 
helix with iron? 

7. How man}' magnetic lines will flow through a helix 
three inches in diameter and five and one-half inches long 
upon the supposition that the magnetic lines meet with no 
resistance except that encountered passing through the in- 
side of the helix; the helix has ninety-five turns and fifteen 
amperes? 

8. If the number of amperes in the helix in No. 7 be 
increased to twenty-one how many magnetic lines will flow? 



79 

9. What is permeability^ 

10. Why is it true that Formula No. 4 is not true when 
iron is used in the ni«agnetie circuit? 

11. When is the permeability of iron low? 

12. When iron contains a great many magnetic lines 
what is said of its magnetic condition? 

13. Why is it that the magnetic circuit of a dynamo is 
almost entirely composed of iron? 

14. How is the permeability table obtained? 

15. What may be said in a general way of the permea- 
bility of wrought iron, common sheet iron, boiler plate and 
cast steel? 

16. Is table No. 4 an exact representation of the per- 
meability of any particular sample of wrought iron or 
steel? 

17. In a general way what are the permeabilities of 
cast and wrought iron? 

IF. In calculating the number of ampere turns requir- 
ed for a magnetic circuit why is it usual to calculate the 
number in each part of the circuit and add them together? 

19. How many ampere turns will be required to force 
1,300,000 lines around the magnetic circuit shown in Fig. 
35? 

20. Give ampere turns required in half of yoke, in pole- 
piece, air gap, body of armature teeth, neck of armature 
teeth and in armature. 

21. How many ampere turns will be required in each 
field coil in Fig. 34, provided 2,300,000 lines of force flow? 
Give ampere turns in each part of the magnetic circuit as in 
preceding question. 



80 

22. Why is it necessary to be more careful in calculat- 
ing the dimensions of the air gap than with other parts of 
the magnetic circuit? 

23. If a field core is made of cast steel, what will be its 
sectional area as compared with a core made of cast iron 
capable of carrying the same number of lines? 

24. How many ampere turns will be required to force 
1.000,000 lines around a.ring averaging one foot in diameter, 
having a sectional area three and one-half inches in diame- 
ter? 




Figure 35 



81 

25. What, besides iron, are the mag-netic metals? 

26. Are the copper and insulation used on an armature 
more permeable than the air which they displace? 

27. What is a smooth core armature? 

28. What are the advantages of iron clad armatures? 

29. What is the effect of using a toothed armature on 
the distribution of lines of force passing from the pole 
piece? 

30. What is the area of the air gap in a dynamo having 
thirt3'-six teeth in the armature, one-third of the arm-ature 
teeth under each pole; the armature teeth .310 inches wide 
at the top, the air gap one-sixteenth of an inch wide and 
five inches long? 

31. How many ampere turns wdll be required in the 
air gap to produce a flux of 5,000 lines crossing the air gap 
between the poles of a horseshoe magnet and its armature 
where the area of the face of the magnet is one-half of one 
square inch and the air gap is one-fourth of an inch long? 

32. W^hat is the usual flux employed in the bottom of 
armature teeth? 

33. W^hat will be the effect of reducing the ampere 
turns ten per cenit. in the motor shown in Fig. 29? 

34. Why is it that the number of magnetic lines which 
flow through an air gap is proportional to the ampere turns 
acting on the air gap, while the number of magnetic lines 
flowing through the rest of the magnetic -circuit is not pro- 
portional to the ampere turns? 

35. Why is it impossible to obtain a'bsolutely correct 
results in calculating the ampere turns required for the 
ampere turns of a magnetic circuit? 



CHAPTER V. 



MAGNETIC TRACTION. 



It is a well-known fact that the north and south poles 
of two magnets attract each other. In fact, the magnetic 
lines act as if they were elastic cords that always tend to 
shorten themselves. When a great number of the magnetic 
lines flow across a given space the attraction is very strong. 

Ewing, in some of his experiments, pushed the mag- 
netism of a piece of soft iron to such a point that the pres- 
sure due to the magnetic attraction was 1,000 pounds per 
square inch. 

Table jN'o. VII gives the pull between a magnet and its 
armatTire when the given fluxes pass. The formula from 
which this table was calculated is 

B2 A 

Pull in pounds equals (7) 

72,134,000 

in which B equals the flux in lines per square inch, A equals 
the area of cross section between magnet and armature in 
square inches. 



^1 

83 

TABLE Xo. VII. 

Flux per sq. in. between Pull in lbs. per sq. in between 

armature and magnet. armature and magnet. 

5,000 .34 

10,000 1.4 

15,000 3.1 

20,000 5.5 

25,000 8.7 

30,000 12.5 

35,000 20.0 

40,000 22.2 

45,000 28.1 

50,000 34.6 

55,000 * 41.9 

60,000 49.9 

65,000 58.5 

70,000 67.9 

75,000 78.0 

80,000 88.7 

85,000 100. 

90,000 ' 112. 

95,000 125. 

100,000 138. 

105,000 153. 

110,000 168. 

115,000 133. 

120,000 199. 

325,000 216. 

130,000 234. 

135,000 252. 

140,000 272. 



84 




Figure 36 
Best forms of magnet for 
lifting purposes. 



The best form of magnet for traction or lifting pur- 
poses is shown in Fig*. 36. 

Fig". SO shows n cross sec- 
tion of a magnet and its ar- 
mature. In this case it is de- 
sired to force a'S many lines 
of force as possible across the 
joint between the armature 
and magnet and also to re- 
duce this area as much as 
possible, for it must be Kept in mind that if we can get the 
same flux across a joint that has an area of 6 square inches 
as flows across another joint having an area of 12 square 
inches, the pull in pounds in the first case will be twice 
what it would be in the second case. This is because the 
pull is proportional to the square of the number of lines 
per square inch flowing. 

A magnet shaped as in Fig. 36 is easily and cheaply 
made and by its shape protects the winding inside it. 

The writer designed a set of magnets for fastening a 
drilling machine to the bottom or sides of an iron vessel. 
These magnets, which would lift from 1,000 to 1,200 pounds 
each, weighed 11 pounds each. 

A flux of 140,000 lines is as high as it is possible to go 
with ordinary steel, and higher than some steels will carry. 
Assuming- that we have steel that will carry 140,000 lines, 
we would have a pressure of 272 pounds per square inch. 
Allowing 100,000 lines per square in. in the rest of the mag- 
netic circuit and 140,000 at the joint between the armature 
and field, what will be the lifting power of a magnet 9 
inches in diameter? 



85 



First, assume the magnetizing coil to be one inch wide 

b3' two inches deep. (Fig*. 37). 

The sizes must be so selected 

that the area of the outside of 

the magnet equals that inside 

the magnet, for as many lines 

pa'ss into the arma-ture outside 

the coil as pas-s out of it inside 
the coil. 




Figure 37 
Pull of iron clad magnet. 



The sizes indicated do this very nearly; the area of 
each part is equal to the area of a circle 5^4 inches in diam- 
eter. Table No. 13 gives this as 21.65 square inches. At 
100,000 lines per square inch there would be 2,165,000 lines 
in the magnet. 

If the surface is cut awa^', as indicated, so as to compel 
the lines to pass into the armature at a density of 140,000 
lines per square inch, the area of contact will be 



21.65x10 



14 



equals 15.5 sq. in. 



As the pull across this surface is 272 pounds per square 
inch, the total pull on both poles of the magnet will be 
15.5x272x2 equals 8,432 pounds. 

The thickness of the armature should be such that the 
lines as they flow from the outside toward the center, as 
shown in the sketch, should never be crowded to more than 
100,000 lines per square inch. In the magnet shown in Fig. 
37, 1he point in the armature at which the lines will be 
most crowded wull be a circle 5l^ inches in diameter directly 
under the south pole of the magnet. 



r 



86 

The surface across which the lines pass is an area eqnal 
to the circumference of a circle 5% inches in diameter or 
16.5 inches x the thickness of the armature. Since the area 
will have to he 21.65 square inches the thickness will be 
21.65 divided by 16.5, or very nearly 1 5-16 inches 

A magnet of this shape is used in some of the electric 
brakes used on some of the suburban cars. 

Here the armature constitutes part of the wheel on 
which the car runs, and the magnet is sta'tionary. 

When current is thrown -into the magnet it attracts the 
armature or wheel, thus tending to lock the wheel. 

There is enough residual magnetism tin the iron to hoid 
the car at a standstill on an ordinary grade without the 
use of hand brakes. 

Magnets are coming into general use for many pur- 
poses. They are used in some rolling mills for handling 
heavy steel ingo«ts and for loading boiler plate on to ears, 
and will doubtless find a greater use as their capabilities 
become better known. 



QUESTIONS ON CHAPTER V. 



1. What is mag'netic traction? 

2. How great a pressure per square inch has 'been pro- 
duced by magnetic traction? 

3. Suppose only a small number of ampere turns can 
be secured to attract an armature, why is it that enlarging 
the pole pieces and armature and therefore the air gap in- 
creases the pull? 

4. Why is it that the area of contact between the arm- 
ature and magnet in Fig. 33a was reduced in order to in- 
crease the magnetic traction? 

5. A certain wheel on an inter-urban street car carries 
a weight of five tons; a pressure of one and one-half torts 
is required on the brake shoe in order to make this wheel 
slide on the rail; design as light a magnet as possible, one 
foot or less in diameter, that will give the pressure between 
magnet and car wheel when car wheel is used as tlie arma- 
ture to make the wheel slip on the track. 

6. A solenoid of the shape shown in Fig. 38 has an 
armature shaped like a horseshoe; how many amperes will 
have to flow through the solenoid in order to lift 100 pounds 
provided the iron core of the solenoid is two inches in diam- 
eter and there is a space of one inch between the stationary 
and movable iron parts of the magnetic circuit? 

7. AVhat is the best shape for a magnet for lifting pui^ 
poses? 



r 



88 



8. How many ampere turns will be required to produce 
a lifting power of 2,500 pounds in an iron clad magnet six 
inches in diameter, provided the slot for the coil is three- 
fourth inches wide and the surface between the armature 
and the magnet is SO per cent, of the sectional area of the 
magnet? 




Figure 88 



CHAPTEK VI. 



MAGNETIC LEAKAGE. 



In dealing with the calculation of the magnetic circuit 
it must be clearly kept in mind that all the magnetic lines 
do not pass through the magnetic circuit as calculated. 
The air will carry lines of force and does carry a great 
many. The magnetic lines that are generated by the fjekl 
coils and that do not pass around the magnetic circuit and 
through the armature are called leakage lines. 

In the tw^o figures (39 and 40) are show^n the paths of 
the leakage lines in two styles of dynamo. 

©_ 



V 




Figure 39 
Magnetic leakage in bipolar dynamo, horseshoe type. 



J 



90 



In the Edison machines as actually made the leakage 
coefficient is 1.4. That is, out of 140 lines produced in the 
field cores only 100 pass throug*h the armature. 

In the other style of bipolar machine the leakage co- 
efficient is less than 1.1. The reason that it is so much 
lower is that only a small surface of fully charged pole is 
exposed to the air. 

In the case of the Edison dynamo Fig. 39) the very 
large pole pieces N. and S. are exposed to the air and al- 
most the full number of ampere turns tend to drive lines 
from ^'. to S. through the air gap and armature and also 
through the air. In Fig. 40 not 1-10 the surface in propor- 
tion is exposed for leakage. 




Figure 40 
Magnetic leakage in internal pole bipolar frame. 

Another great advantage of the internal pole type is 
that what leakage there is is inside the machine, where it 
is not apt to draw wire nails and bits of iron dust; but in 
the case of the Edison dynamo the magnetic leakage will 
attract all the iron that comes in its neighborhood, and 
there is danger of pieces of iron being drawn into the arma- 
ture. 



91 



TABLE No. VIII. 



Diagrams of magnetdc circuits of several dynamos and their 
leakage coefficients. 




Diagram of magnetic circuit of Edison dynamo. 
Leakage coefficient 1.4. 




Diagram of magnetic circuit of T. H. bipolar dynamo. 
Leakage coefficient 1.3. 



^WilSMi 






Diagram of magnetic circuit of Westlnghouse 4-pole dynamo 
Leakage coefficient l.l. 



92 




Diagram of magnetic circuit of Lincoln 2-pole dynamo. 
Leakage coefficient 1.1. 




Diagram of magnetic circuit of G. E. 14-pole alternator dynamo. 
Leakage coefficient 1.25. 




Diagram of magnetic circuit of Siemans & Halske dynamo, 
4- pole field inside armature. Leakage coefficient 1 08. 




Diagram of magnetic circuit of Manchester type. 
Leakage coefficient 1.5. 



QUESTION'S ON CHAPTER VI. 



1. What is magnetic leakage? 

2. What is the relative conductivity of air and iron as 
used in a dynamo for. magnetic lines? 

3. How is it possible to design a machine so that the 
magnetic leakage will be reduced to a minimum? 

4. Why is it that an Edison dynamo has so many more 
leakage lines than an internal pole machine such as shown 
in Fig. 36? 

5. In Fig. 25 it was assumed that all the lines jlowed 
through the iron teeth into the armature. How many lines 
will leak through the slots occupied by the wire? 

6. How many lines will leak across the space in which 
the armature revolves if the armature is removed in Fig. 29? 

7. Why is it that there is such a great amount of mag- 
netic leakage and so small an amount of electric leakage in 
ordinary circuits? 

8. Does the fact that a dynamo has great magnetic 
leakage impair its efficiency greatly? If so, why? 

9. Name other disadvantages of magnetic leakages. 

10. What are the advantages of the internal pole type 
of machines as compared with the horseshoe magnet type? 

11. What is a coefficient of leakage? 



CHAPTER VII. 

ENERGY IN ELECTRIC CIRCUITS. 

It is a well-known fact that when current flows through 
an electric circuit in sufficient quantity heat is developed. 
The incandescent lamp is the most ordinary example of this. 
Experience will prove that doubling- the amount of current 
through a resistance without changing the voltage doubles 
the heat produced in The resistance. Also doubling the 
voltage tending to drive current through resistance without 
changing the current doubles the heat produced. This 
may be very easily proved by making the experiments indi- 
cated in Figs. 41, 42 and 4o. 




Figure 41 
Certain heat produced in lamp 




no VOLT 5 



Figure 42 
Twice as much heat with same 
voltage and twice the current. 




VOLTM 



Figure 43 

Twice as much heat as Figure 37 with double voltagt 

and same current. 



95 

It is clear that the energy in the electric circuit is pro- 
portional to the current and also to the voltage or to the 
product of voltage and current. 

Energy in' an electric current is measured in watts, and 
we may write watts equals amperes x volts, or 
W equals CxE (8) 
Substituting in (8) its value from Ohm's law C equals 

E 

K 
— (See Chap. I.) 

We have 

E E2 

W equals — xE equals — (9). 
R R 

Again substituting in (8) the value of E from Ohm*s 
aw equals CxR. 

W equals CxCxR equals C2R (10). 

Putting (8), (9) and (10) in words: 

Watts equals amperes x volts (8). 
Watts equals (volts x volts) divided by ohms (9). 
Watts equals amperes x amperes x ohms (10). 
746 watts equals one horse power. 

These formulae should be carefully studied and thor- 
oughly committed to memory. Suppose it is required to 
(ind how many horse power a certain motor is using from 
the circuit supplying the power. First measure the voltage 
at which current is delivered, next measure the current. 

Suppose a circuit supplying power has 240 volts 



96 

and that a motor is taking* 15 amperes. From formula 
(8) we have watts equals 240x15 equals 3600 watts. The 
horse power equals the fwatts divided 'by 746, or H. P. equals 
?.600 divided by 746 equals 4.83. 

Suppose the same current was used in a (healer or a 
wire resistance, the resistance would be 

E 240 

R equals — equals equals 16. 

€ 15 

If now formulae (8),' (9) and (10) are correct, all three 
should give the same result in watts. We have 

Amperes equal = 15 

Volts equal 240 

Ohms equal 16 

Watts equal 3600 

Formula (8) Is watts equals amperes x volts equals 
15x240 equals 3600. 

Formula (9) is watts equals volts x volts divided by 

240x240 

ohms equals equals 3600. 

16 

Formula (10) is watts equals amperes x amperes x 
ohms equals 15x15x16 equals 3600. 

If the sbunt field coil of a djmamo takes 2% amperes at 
200 volts, what is its resistance and how many watts is it 
using? 

E 200 

Ohms equals — (3) equals equals 80. 

C 2.50 

Watts equals Ex)C equals 200x2 Vi equals 500 or about 2-3 

H. P. 

y 



97 

If a series dynamo has 10 amperes flowing" through its 
field and the resistance of the wire is 3.6 ohms, how many 
watts is it using" and how many volts are required for this 
part of the circuit? 

Volts equals CxR (2) equals 10x3.6 equals 36. 

Watts equals C^R equals 10x10x3.6 equals 360, or a little 
less than y^ H. P. 

Suppose the current in a long distance power transmis- 
sion plant is 300 amperes and that the voltage at the receiv- 
ing end is 750 volts less than at the sending end, what is the 
resistance of the line and how many H. P. are lost due to 
the resistance? 

E. 750 

R equals — (3) equals equals 21/2 ohms. 

C 300 

Watts equals CxE (12) equals 300x750 equals 225,000. 
H. P. equals 225,000 divided by 746 equals 301.6 H. P. 

If the voltage at the sending end was 10,000, what was 
the proportion of power delivered to that received? 

Power delivered to line, watts equals 300x10,000. 

Power received from line, watts equals 300x9,250. 

925 

Ratio equals equals 92.5%, or efficiency of trans- 

1000 
mission line. 

Why is it that high voltage is used in all the long dis- 
tance power transmission plants? A study of formulae 
(8), (9) and (10) will answer this question. 



98 

Suppose it is desired to transmit 50 H. P. five miles. 
The watts will be 50x746 equals 37,300. If this is generated 
at 250 volts the current will be 37,300 divided by 250 equals 
149 amperes. 

If the line has a resistance of J/^ ohm, the volts lost in 
the line will be 149xy2 equals 74.5. The efficiency of trans- 
mission will be 

(250— 74.5)x300 175.5 

equals or about 70 per cent. 

250x300 ' 250 

That is, 30 per cent, of the power is lost in the line- 

If now the same power be generated at 500 volts, %he 
amperes will be 37,300 divided by 500 equals 74.5 a eres. 
The volts lost on the line will be yox74.5 equals 37.25. The 
efficiencj^ of transmission 

(500— 37.25)x74.5 

equals 92.50 

500x74.5 

In this case only 7yo% of the power was lost. If we 
should repeat the calculation at 1000 volts we would see 
thnt only y^ of 7y2% would be lost, or less than 2%. That 
is, 50 H. P. transmitted at 250 volts loses 30%, and at 1000 
volts less than 2%. 

The power lost in transmission is inversely proportional 
to the square of the voltage with a given line. 

The use of high voltage enables a small and cheap line 
io transmit the same power with the same loss that a line 
with iuur limes as much copper in it would transmit with 



V 



99 

the same loss at half the voltage. A little thought will show 
that the line loss is proportional to the square of the dis- 
tance from the generating station if equal amounts of cop- 
per are used in ail the lines. Thus a line one mile long 
having 1000 pounds of copper will have a resistance of .85 
ohms; a line two miles long having the same 1000 pounds 
of copper in it will have a resistance of 3.4 ohms, or four 
times as much. If the same current is sent over both lines 
there will be four times as much loss in the two-mile line 
as in the one-mile line. But if. at the same time that the 
length of the line is doubled the voltage is also doubled, 
100 H. P. can be transmitted over the long line with the 
same loss as o\er the short one. Thus, with a given line 
loss and a given amount of copper in the line, the distance 
to which power can be transmitted is directly proportional 
to . voltage. 

^ In calculating watts lost in an armature, it is necessary 
usually to find the current flowing through it and find the 
resistance of the armature and use these two factors to find 
the watts lost. 

LofC. 



QUESTIONS ON CHAPTER VII. 



1. What are the three formulae representing power in 
an electric circuit? 

2. How many watts are there in one horse power? 

3. How many watts are expended in a circuit feeding 
a number of heaters if the currrent is eight amperes and 
bhe E. M. F. 500 volts? 

4. How many amperes are flowing in a circuit which 
consumes five and one-half horse power at 110 volts; at 
1.000 volts? 

5. What is the resistance of a feed wire in which eight 
H. P. are lost when 300 amperes are being carried by the 
line? 

6. What H. P. is developed by a dynamo which delivers 
400 amperes at 250 volts? 

7. What is the per cent, drop in a feed wire in whiah 
five H. P. are lost when 250 amperes; are flowing, and the 
dynamo producing the current 'has an E. M. F. of 300 volts? 

8. Is it possible to determine the resistance of the arm- 
ature in question 6 from the data given in that question? 
If so what is the resistance? 

9. How much current is used on a lamp that requires 
64 watts on a 110 volt circuit? 

10. How mai:y amperes equal one H. P. on a 110 volt 
circuit? On a 220 volt circuit? On a 500 volt circuit? On 
a 1,000 volt circuit? On a 10,000 volt circuit? 



101 

11. How many amperes are there in a kilowatt or in 
1,000 watts or in a K. W. in circuits of each of the voltag"es 
specified in question 10? 

13. Why is it that the Edison three-wire system is 
economical of copper? 

13. Would a five-wire system on the same plan be more 
or less economical? Why? 

14. Why is high voltage used for distributing power to 
great distances? 

15. Would it be practicable to transmit 100 H. 
P. over a line having three and one-half tons of copper in 
it to a point fi.ve miles away if 250 volts were used? 

16. Would it be practicable with 500 volts; with 1,000 
volts; with 20,000 volts? 

17. Why is it that that with the same cost for copper 
the power loss increases as the square of the distance from 
the power station? 

IS. In what ratio does the loss of power decrease with 
increasing voltage, cost for copper remaining the same? 

19. What is the ratio of distance to which power may 
be transmitted and voltage of supply with constant cost for 
copper and constant line loss? 

20. Wliat will be the cost for copper at .15 per pound 
for a line that will transmit power for 500 — 55 watt, lamps 
at 250 volts on a three-wire system perfectly balanced 14 
mile from dynamo if current is supplied to lamps at 110 
volts? 



102 

21. Suppose a dj^namo is supplying a power circuit at 
125 volts and it is desired to light 300 — 55 watt lamps at a 
pressure of 110 volts 2,500 feet away. Tw^o methods can be 
used for lighting these lamps; a large wire can be run from 
the dynamo to the lamps, in v^hich there will be a drop of 
15 volts. A second method is to drive a 650-volt dynamo 
from the same engine that drives the 125-volt dynamo, op- 
erate a motor on the 650-volt current and drive a second 
dynamo working at 110 volts to light the lamps. If copper 
costs .15 per pound, and three extra electric machines cost 
$1,500, which will be the cheaper installation? 

22. If one horse power is lost in 1,000 feet of No. 0000 
vdre with a drop of 35 volts, what current is the feeder car- 
rying? 

23. . Why is it that in calculating the number of watts 
lost in an armature that formula No. 14 is usually employed? 



CHAPTER VIII. 

CALCULATION OF MAGNET COILS. 

As shown in the chapter on the magnetic circuit it is 
possible to find how manj^ ampere turns are required to 
force a g-iven magnetic flux over a given magnetic circuit. 
After it is discovered in this way how many ampere turns 
each coil should produce, it is necessary to select the size of 
wire and determine the amount that should be used to pro- 
duce the desired result. 

The magnetizing power of any coil is measured in 
ampere turns, or the product of the amperes w^hich flows 
through the wire, multiplied by the number of ximes it cir- 
culates arour^d tlie core. The meaning of the term is al- 
most self-evident. 

A very peculiar fact becomes apparent upon examining 
the number of ampere turns produced b}' a given coil when 
exposed to the same voltage. Take, for instance, a coil 
wound aj'ound an iron core 3^4 inches in diameter; let the 
thickness of the magnetizing coil be such that the average 
diameter of the coil will be 3% iuches, so that the average 
length will be one foot. If this coil is wound with one 
pound of No. 16 wire it will have, as shown by Table 1, 124 
turns. 

The resistance of such a coil will be .515 of an ohm. 
If such a coil is exposed to a pressure of 50 volts, 97.1 
amperes will .flow through it, and the ampere turns pro- 
duced by the coil wil! be 97.1x124, or 12,040. 



104 

If twice as much wire be used on this coil, the ampere 
turns will not be twice as great as might be expected, but 
will remain the same. The only dilt'erence will be that 
instead of 07.1 amperes liowing through the coil, only half 
of this, or 48.55 amperes will flow. 

It will be seen that doubling the amount of ^^^re on a 
coil has doubled the number of turns, but also doubled 
the resistance of the coil so as to reduce the current to one- 
half. 

The product of double the number of turns multiplied 
by half the number of amperes which we have in the sec- 
ond coii produces the same number of ampere turns as 
were produced by the first coil. Increasing the weight of 
the coil then simply decrease the amount of current re- 
quired to produce a given number of ampere turns. 

To produce a greater number of ampere turns in this 
same coil, it will be necessary to wind the coil with larger 
wire, or to increase the voltage applied to the terminals of 
the coil. By using a wire of twice the sectional area of 
No. 16, double the number of ampere turns will be pro- 
duced, or if the average length of the coil instead of being 
one foot is tv/o feet, a wire of double the sectional area of 
No. 16 will be required to x>roduce 12,040 ampere turns at 
50 volts. If at the same time that the average length of 
the turn was increased from one foot to two feet, the volt- 
age was raised from 50 volts to 100 volts,^ No. 16 wire w^ould 
still continue to produce 12,040 ampere turns. 

Putting these considerations into the form of an equa- 
tion we have: 

llVoxATxL 
A equals 



105 



in which A is area of the wire in circular mils or is the 
square of the diameter in thousandths of an inch. 

A. T. equals ampere turns, L equals average length of 
one turn of the magnetizing coil in feet, E equals pressure 
in volts. 

Take the Edison machine shown in Fig. 28^ Suppose 
it is a 220-volt motor. It is found that 11,074 ampere turns" 
should be produced by each coil to force the desired flux 
around the circuit. 

Let us assume that the coil will be two inches thick. 
It is not good practice to make them much thicker than 
this, because if they are the heat cannot get away from the 
inner layers out to the air through the outer layers. This 
makes the average length of the turn the circumference 
of a circle 10 inches in diameter, or 31.41 inches long, o^* 
2.62 feet long. 

E equals 110 volts, for the motor works on a 220-volt 
circuit and is provided with two coils connected in series. 

11.5x11074x2.62 

A equals equals 3040 

110 

Exanjination of Table 1 shows that this is between No. 
15 and No. 16 wire, and we will select No. 15 as being the 
size required. If it is desired to know just what number 
of a. t. No. 15 will produce, find how many turns one pound 
will make, or 101.63 divided by 2.62, or 38.8 turns per pound. 

A one-pound coil will have a resistance of .32 ohms per 
pound, and a coil made of a single pound will allow 110 
divided by .32 or 344 amperes to pass. The ampere turns 
of this size will then equal 38.8 x 344 equals 13,347 ampere 
turns. 



106 



It should be carefully kept in mind that the amount of 
wire on a coil simply determines whether it shall run cool 
or hot; the size of the wire determines the number of am- 
pere turns. 

The formula is arranged o-n the assumption that the 
average temperature of the magnetizing coil is 125 degrees 
Fahrenheit. This assumption gives a larger wire than 
would be necessary if the coil operated at a lower tempera- 
ture, because the resistance of copper wire increases .21 
of one per cent, for each degree Fahrenheit rise in tem- 
perature, and if the magnetizing coil could operate at an 
average temperature of 75 degrees Fahrenheit instead of 
125 degrees, the resistance of the coil would be 10% per 
cent, less, and its magnetizing power 10y2 per cent, greater. 

If, however, the average operating temperature of the 
coil is above 125 degrees Fahrenheit, the size of the wire 
will be too small rather than too large, because the resist- 
ance pf the wire composing the magnetizing coil will be 
greater than that assumed in the formula. 

Wire enough should be put on the coil so that the 
watts lost will not be over .8 per square inch, and much 
more satisfactory results will be obtained if enough are used 
so that only .5 watts will have to be radiated per square 
inch. 

In the coil for the Edison dynamo the radiating surface 
is 10 inches x the circumference of a circle 12 inches in 
diameter, or 10x37.64 equals 376.4 sq. in. WTiile a large 
part of the heat radiated from the coil will escape from the 
outside, almost as much will be radiated from the ends of 
the coil and into the iron core inside. The iron core will 
conduct the heat to the heavy pole piece and yoke, where 
it is quickly radiated. 



lOV 



It is safe to allow three-fourths as much radiating sur- 
face for the rest of the coil as it has direct radiating sur- 
face, so the total radiating'surface is 3764-% (376) equals 658 
square inches. At ^ watt per square inch we have wasted 
in this coil 329 watts, and at 110 volts this means a current 
of 329 divided by 110 equals 3.0 amperes. 

We have seen that if the coil has only one pound of 
wire 344 amperes will flow. If only three amperes are 
wanted, we will have to make the coil weigh 344 divided by 3 
equals 115 pounds. The final result as to the winding for 
the magnetizing coil for the Edison dynamo is then 115 
pounds of Xo. 15 B. & S. wire. 

The next question is, will the space allowed for the 
winding take so much wire as this? 

The cross section of the coil was 2 inches x 10 inches and 
the average length of each turn was 2.62 feet. The number 
of turns in each layer would be 10 inches divided by .065, for 
No. 15 wire is .057 under the insulation and will be about .065 
over the inr.ulation if single cotton-covered wHre be used. 

10 divided by .065 equals 153 turns per layer. 

The number of layers will be 2 divided by .065 equals 31. 

The number of feet on the coil will be 153x31x2.62 equals 
12,427 feet. 

Table No. 1 shows that single cotton-covered magnet 
wire weighs 10.13 pounds per 1000 feet, and 12,427 feet will 
weigh 12.43x10.13 equals 126 pounds. We can get in 126 
pounds of wire in the space that 115 pounds should be put in. 



108 



What sized wire and how much should be used to wind 
the ironclad dynamo shown in Fig. 31. Here the ampere 
turns required are 2791; the 
coil was 3 inches wide x 2 
inches thick. The average 
length of this coil may be 
found from Fig. 44. The aver- 



age length of the turn is 

6 plus 2^3 plus 6 plus 21/2 plus 

(3.1416x5) 
or the circumference of a cir- 




6^-H 



^z^^- 



T^ 



J 



cle 5 inches in diameter equals Dimension s?f mag ilti zing coil- 

32.7 inches equals 2.72 feet. average length of turn. 

Suppose this is to be a 500- . 

volt motor, then each of the two coils w^ill be exposed to 250 

olts. 

Substituting in the formula, we have: 

IIV. x ?789 x 272 

A equals equals 337.8 

250 

or a little larger than No. 25. 

>^o. 24 will have to be used. 

No. 24 or .020 wire has 819.2 feet per pound, and 819.2 
divided by 2.72 equals 301 turns per pound. Also it has 21 
ohms per pound and a one-pound coil allows 250 divided by 
21 equals 12 amperes to pass; 12x301 equals the ampere 
turns of No. 24 wire equals 3612. 

The coils for this motor are wound on forms and 
slipTjcd over the pole piece. This allows all the outside and 
both sides to rafjiate heat, and we may allow one-half the 
inside surface of the coij as a radiating gijrface. 



109 

Radiating surface equals (32.7x2x2)-f(39x3)+y2 (26.5x3) 
equals 28S square inches. At Vo watt per square inch the 
current will be 144 divided, by 250 equals .58 amperes. 

If a one-pound coil passes 12 amperes, the coil must 
weigh 12 divided b^^ .58 equals 20.6 pounds to cut the current 
down to .58 amperes. 

The winding for the magnetizing coil for the motor in 
Fig. 25 for 500 volts is 20.6 pounds of No. 24 wire. 

It is clear that in a coil exposed to a constant potential 
the size of the wire and not the amount of wire or number 
of turns is what determines the magnetizing power. 

In a constant current dynamo, such as one used for arc 
lighting, the number of turns determines the magnetizing 
power, and the size of the wire simply determines the 
amount of heating or the energy wasted in the coil. 

In a coil using constant current it is only necessary to 
divide the number of ampere turns required by the number 
of amperes. This gives the turns required. Then select a 
wire of such size that the coil will not get too warm. 

The same rule should be followed in calculating the size 
of wire required for the series coil of a compound wound 
dynamo. It should be kept in mind that the heating of a 
shunt coil on a constant voltage raises the resistance and 
prevents more current from flowing, thus tending to pre- 
vent the coil from over-heatmg. 

In the series coil the reverse is true, for the heating of 
the coil makes the resistance higher and so increases the 
heating with a given current. 



QUESTIONS FOB CHAPTER VIII. 



1. In calculating the ampere turns for a magnetizing 
coil of any given size of wire, what is the first thing neces- 
sary to know^ abont the dimensions of the coil? 

2. Describe how^ the number of ampere turns that will 
be produced by a coil of given. dimensions and size of wire 
may be determined. 

3. How many ampere turns will be produced by a coil 
whose average diameter is 10 inches, size of wire No. 20, coil 
exposed to an electro-motive force of 110 volts? 

4. What size of wire will be required to produce the 
same number of ampere turns as in preceding question at 
271/2 volts? 

5. How many ampere turns will be produced in a coil 
having an average length of turn of 4 inches if the voltage 
used is 110 and the wire used is No. 20? 

6. Why is it advisable when only a small amount of 
electrical energy is available for the purpose of magnetizing 
a small horse-shoe magnet to make the coil long and thin? 

7. Why are such large magnet cores used in commer- 
cial dynamos? 

8. When a coil is exposed to a constant electro-motive 
force why does the size of the wire and not the amount of 
the wire in the coil determine the ampere turns produced 
by the coil? 

9. Is there any reason for using a coil of considerable 
weight rather than using one weighing only a few pounds? 



Ill 



10. What size of wire will be required on the motor 
shown in Fig. 31 for a siix-volt plating dynamo; for 110, 220, 
and 500-volt motors? 

11. What weight of wire will be nsed in the coils cal- 
culated in the preceding question if 1/2 of a watt be radiated 
for one square inch of the surface of the coil? 

12. How many watts per square inch is it safe to allow 
the coil to radiate? 

13. Why is it not advisable to use a ooil more than two 
inches in thickness? 

14. How much does the resistance of copper wire in- 
crease on account of the increase of the temperature? 

15. How is it possible to determine the number of 
pounds of wire that will be required in a coil to reduce the 
current consumed to a given amount? 

16. Calculate the size and weight 'of the wire required 
for a 250-volt motor of the dimensions calculated in answer 
to question 19, chapter V. 

17. Calculate the size of wire and weight required for 
the magnetizing coils in Fig. 31, provided they radiate l^ 
watt per square inch when used as a 250-volt dynamo. 

18. How are the ampere turns for a series coil calcu- 
lated? 

19. What is the effect on the power wasted in a coil, 
of the raise in temperature in a coil exposed to a constant 
voltage? 

20. What is the leffect in a coil through which a con- 
stant current flows? 



r 



CHAPTER IX. 

WINDING ELECTRIC MACHINERY FOR DIFFERENT 

E. M. Fs. 



It was explained ?n Chapter IV that E. M. F. is pro- 
duced by a wire cutting lines of force, and it was also stated 
that where magnetic lines are cut at the rate of 100,000,000 
per second, one volt is produced. Fig. 45 shows the cut- 
ting of the lines of force in a Gramme ring armature and 
also the path of the lines. Fig. 40 shows the cutting in the 
internal bi-polar machine shown in Fig. 31. 



' r*Pl 




® 




rt-l 


' 




N 

S 








i 


1 













Figure 45 
Production of E. M. F. in Gramme ring armature. 



113 



la the gramme ring armature the lines cross the air 
gap and pass around the ring from theN. pole to the S. pole. 
When the armature revolves, there is a constant movement 
of the magnetism in the armature. A few of the magnetic 
lines leak across the space inside the ring, as shown in the 
sketch. 




Figure 46 
Production of E. M. F. in drum armature. 



By applying the rule on page 47, we see that the cur- 
rent tends to flow toward the observer in the wires in the 
air gap in the lower part of the armature. 

The same rule shows that the current flows away from 
the observer in the upper part of the armature. A little 
thought will show 'that if the winding on the ring is a con- 
tinual spiral, these two currents will meet each other at 
points marked -|- and — about half way between the poles. 

If the spiral be connected at regular intervals to the 
bars of a commutator and two brushes touch this commu- 
tator at points on a horizontal line, there will be an E. M. F. 
between these two brushes equal to the sum of the E. M. F.'s 
produced in all the wires under one pole. 



Suppose the armature revolves 1200 turns per minute; 
this will be 1200 divided by 60 equals 20 
revolutions per second. Also suppose there are 
1,000,000 lines of force flowing from the N. pole into 
the ring through the ring into the S. pole. Each 
wire on the armature will cut 20 times per second the 
1,000,000 lines in the upper air gap, and therefore each wire 
cuts 20x1,000,000 equals 20,000,000 lines per second. 

Since it requires cutting at the rate of 100,000,000 per 
second to produce one volt, each wire on the armature pro- 
duces 

20,000,000 

equals 1-5 



100,000,000 



of a volt in passing through the upper air gap. The same 
wire produces the same voltage in the opposite direction in 
its passage through the lower air gaj), but the two halves 
of the armature are in parallel. The E. M. F. produced may 
be illustrated by the diagram in Fig. 47. 




Figure 47 

Production of E. M. F. in an armature illustrated by two groups 

of batteries placed in paralJol. 



115 



In Fig. 47 if each cell produces two volts, the whole 12 
cells produce only 12 volts, but the capacity for delivering 
current is doubled. The same thing is true of the dynamo 
armature.. There are always two voltages produced which 
are placed in parallel. This fact makes the carrying capac- 
ity of an armature for current always equal to twice that 
of a single wire of the size the armature is wound with. 

If there are 550 wires or 550 turns on the armature in 
Fig. 41, the E. M. F. produced will be 550 times that pro- 

550 
duce in one wire, or equals 110, or, in the form of an 



equation: 



1,000,000x550x20 

E. M. F. equals equals 110 

100,000,000 

In symbols this becomes: 

NxTxS 

E. M. F. equals — (11) 

100,000,000 

Transforming (11) to get the other quantities: 

E. M. F. X 100,000,000 

N equals (12) 

TxS 

E. M. F. X 100,000,000 

T equals (13) 

NxS 

E. M. F. X 100,000,000 

S ecuials (14) 

NxT 



f/^ 



116 



Where N equals total number of lines flowhig across 
one air gap, T equals total number of wires on the armature 
that cut lines of force, and S equals number of revolutions 
per second. 

The turns on the inside of the Gramme ring do not cut 
any lines and so produce no E. M. F. 

Tn the case of the drum armature, however, the one 
side of a turn is in one air gap and the other side is in the 
other air gap. Therefore it ife only necessary to have half 
as many turns in a drum armature to get the same E. M. F. 
as are required in a Gramme ring. At first sight it would 
seem that the Gramme ring w^ould require much more wire 
for the same E. M. F. than the drum armature, but each 
turn is much shorter in the Gramme ring than in the drum 
armature. 

A very important practical advantage that the Gramme 
ring possesses is that the w4res do not cross 
each other at the end of the armature. If 
anything is the matter with one coil in a Gramme ring 
it can be removed without touching any of the other coils. 
This is not the case with a drum armature, for coils cross 
each other and It may be necessary to take off all the coils 
in order to get down to the one that is damaged. 

It is easy to see that with a given iron frame and arma- 
ture core the only thing necessary to do to make it develop 
different voltages is to put different numbers of turns on 
the armature. If it was desired in Fig. 45 to produce 220 
volts, it would be necessary to wind on 1100 turns of wire 
instead of 550. 



117 



Suppose there is a flux of 1,200,000 lines in the core 
shown in Fig. 46, that there are 40 coils on the armature, 
that the machine runs 1,500 revolutions per minute. How 
many turns will it be necessary to use for 500 volts, for 220 
volts, and for 110 volts? 

Substituting in (13) 

500x100,000,000 



T equals 

1,200,000x25 

Solving this equation, 

500x100,000,000 

T equals equals 1667 

1,200,000x25 

ThLs is the number lof active oomductors on a Gramme 
ring or drum armature. This will be ihlalf the number of 
turns on a drum armaituTe. The number of turns will be 
1667 divided by 2 equals 834, and since there are 40 coils, 
each coil will contain 834 divided by 40 equals 21 wires. 
Each turn in such a coil contains two wires that generate 
E. M. F. 

The fundamental fact on which the action of the dyna- 
mo depends was illustrated in Fig. 20, and it is excellent 
practice to determine from the direction of rotation of an 
armature and from the polarity of the magnet in any actual 
dynamo the direction in which the current is running on 
the armature. 

It is easy to determine the number of lines of force that 
are flowing across any dynamo armature. 



118 



Suppose an Edison dynamo has 60 coils having- two 
turns each, and that it generates without any load 230 volts 
at a speed of 1200 revolutions per minute. What is the flux 
across the armature? 

In this case 

S equals 1200 divided 'by 60 equiails 20. 

T equals 60x2x2 equals 240. 

Substituting in (12), 

230x100,000,000 

N equals equals 4,792,000 

240x20 

In practice the only difference in dynamos designed for 
the same output at different voltages is the difference in the 
number of turns of wire on the armature. 

Suppose the dynamo is designed for 500 volts with a 
certain number of turns on the armature; for 250 or 220 
volts only half this number is used and for 125 or 110 volts 
only one-fourth as many are used. 

Another way in which the voltage produced in a dyna- 
mo may be considered is the change in number of lines of 
force enclosed or embraced by a coil. 

There will be an E. M. F. generated in a coil propor- 
tional to the rate of cQiamge in tihe number of lines of force 
embraced by the coil. 

If lines of force are put into or taken out of a coil at 
the rate of 100,000,000 per second, one volt is produced. 
The E. M. F. produced by such a change in the number of 



119 



lines embraced by a coil may be determined by Lentz law. 
According to Lentz law the current produced in a closed 
coil by a change in the number of lines of force is always 
in such direction as to oppose by its owm magnetic action 
the change in number of lines enclosed. 

The result is, that when a S. pole is caused to approach 
a closed coil the current in it will flow in such a direction 
as to produce a S. pole in the coil, opposing the approach- 
ing S. pole, and, when the S. pole is being withdrawn, the 
current will flow so as to produce a N. pole in the coil op- 
posing the approaching N. pole. 

In the first case the approaching pole is repelled, and 
in the second, the receding pole is attracted; therefore 
power is required both to cause the pole to approach and 
to recede. 



QUESTIONS ON CHAPTER IX. 



1. How many lines of force is it necessary for a wire to 
cut per second in order to produce one volt? 

2. Explain the production of electro-motive force in a 
g-ramme ring armature. 

3. What is the office of a commutator on a direct cur- 
rent machine? 

4. Why is the resistance of an armature never more 
than one-fourth that of the wire with which the armature 
is wound? 

5. How many volts will be produced in a two-pole ar- 
mature drum wound having 30 slots in the armature if the 
armature is wound with 30 bobbins of 10 turns each and the 
flux across the armature is 1,000,000 lines and the speed is 
1,200 revolutions per minute? How fast would the above 
armature run as a motor on a 150-volt circuit? 

6. Give from memory the four formulae expressing the 
relation between the E. M. F., magnetic flux, the speed and 
the number of turns. 

7. A bi-polar dynamo runs 1,140 revolutions per minute 
and produces 114 volts; there are 36 slots in the armature, 
each bobbin has six turns of wire. What is the magnetic 
flux across the armature? 

About .050 insulation should be used between the wire 
and iron. 



121 

8. A bi-polar motor on a 120-volt circuit is desired to 
run 1,100 revolutions per minute; there are 48 slots in the 
armature and the flux is 2,100,000 lines. Each slot in the 
armature is l^ inch wide and % of an inch deep. H-ow 
many turns will be required in each bobbin and what will 
be the resistance of the armature? 

9. What is it necessary to change about a motor in 
order to make it operate on a circuit of double its voltage? 

10. What is true of the number of turns of wire re- 
quired to produce the same electro-motive force on a 
gramme ring and a drum armature? 

11. What advantage does the method of winding used 
on a gramme ring armature possess? 

12. A bi-polar gramme ring armature is designed to 
run at 1,500 revolutions on 250-volt circuit; there are 56 
sections on the armature, each with two turns. What would 
be the section required in the pole pieces of this dynamo if 
a flux of 40,000 lines per square inch is used? 

13. Why will the resistance of an armature be quadru- 
pled if it is rewound to run at half its original speed '^ 



CHAPTER X. 



COUNTER ELECTRO-MOTIVE FORCE. 



Whenever an armature is revolved in an excited field, 
E. M. F. is produced, whatever be the cause of the rotation. 
The armature may be revolved by a belt from an engine, 
or it maj^ be revolved by a motor directly connected to it, 
or it may be revolved by a current flowing through it in 
such a direction that it becomes a motor. 



tc:^ 




mi|i|i|i|i|i|i|iHi|i|iHi|i|i|i|i|i|J 



Figure 48 
Illustration of the identity of counter and primary E. M. F. 



123 



In the first two cases the E. M. F. produced may be 
measured and used to produce current in an outside circuit 
if desired. In the last case, however, the E. M. F. appears 
as an E. M. F. opposing the E. M. F. of the current that 
drives current through the motor. This E. M. F. is called 
counter E. M. F., because it acts counter to the primary 
or principal E. M. F. That this counter E. M. F. really ex- 
ists may be made clear by a study of Fig. 48. 

In Fig. 48 the source of power is a turbine water wheel 
having a capacity of 100 H. P. This drives a shaft on which 
is a pulley that drives a 175 H. P. dynamo for street railroad 
work. Connected to the shaft is a 75 H. P. dynamo that 
charges a storage battery. The average load on the street 
railway generator is 100 H. P., but it varies from 25 H. P. 
at the lowest to 175 H. P. at the highest. If the main dyna- 
mo is taking at any time 75 H. P., the turbine wheel will 
rise in speed a little and so raise the speed of the motor 
dynamo a few revolutions until the extra 25 H. P. is used in 
producing current that charges the storage battery. 

If, now, two or three cars all start at the same time, the 
load on the main d^mamo may become 150 H. P. This will 
cause the speed of the turbine wheel to drop a little until 
the voltage of the dynamo is a little less than that of the 
storage battery, when current will flow from the battery 
into the armature of the machine, which is now a motor 
until it is developing 50 H. P. 

The electro-motive force of the dynamo now appears as 
counter E. M. F., which tends to prevent the storage battery 
current from flowing throiigh it. 

The scheme here illustrated is practical, and a variation 
in speed of 40 or 50 revolutions in 1200 would change the 



124 



machine from a dynamo charging the storage battery at 
the rate of 75 H. P. to a motor taking power from the bat- 
tery and delivering 75 mechanical H. P. 

It is now easily seen why a current in magnet of start, 
box is so nearlj^ constant in speed. 

The resistance of the armature is very low, so that with 
full load current only a few volts are lost due to resistance, 
and the force that prevents a great rush of current through 
the armature is the Counter E. M. F. of the armature. Con- 
sider equation (14): 

E. M. F.xlOO,000,000 
S equals ^ 

NxT 



This indicates that the speed depends on the E. M. P. 
and will change in the same ratio that it does, for JN, the 
total flux through the armture, will remain constant as 
long as the voltage on the exciting coils does not change, and 
T, the number of turns on the armature cannot be changed 
after the armature is wound. 

The counter E. M. F. plus the volts lost in the armature 
must always be equal to the applied E. M. F., and if the 
resistance of the armature is low, so that only two or three 
volts are lost in it at the heaviest load, the counter E. M. F. 
must remain constant, and if the counter E. M. F. is con- 
stant, the speed must remain the same. 

Looking at this in another way, the voltage forcing 
current through the armature is the difference between 
the applied and the counter E. M. F. 



125 



If a heavy load is thrown on a motor that requires a 
heavy current, the first eft'ect w^ill be to reduce the speed. 
Reduciug the speed lov^ers the counter E. M. F, and this 
causes a greater E. M. F. to force current through the arma- 
ture. 

If the applied E. M. F. is 110 volts and the resistance is 
.01 ohm, and the current required to run the armature with- 
out any load on it is 6 amperes, the counter E. M. F. is 109.94 
volts. If full load is thrown on, which may be 100 amperes, 
the loss of voltage in the armature is one volt and the coun- 
ter E. M. F. is 109 volts. These figures are about what ob- 
tain in practice. Thus by a change of less than 1% in speed 
the motor has taken its full load current. 

In a shunt wound motor the field is constant and the 
speed is consequently almost perfectly constant. In a series 
motor, however, the current that supplies the armature and 
fields is the same, and an3^thing that alters the current in 
tJie armature alters the current in the field and changes 
the flux through the armature. 

Figs. 49 and 50 show a diagram of the winding of a 
shunt and series motor respectively. 



— [ _i -^ 



Figure 49 
Diagram of connections of shunt motor. 



126 



In the shunt motor the amount of current passing 
through the armature does not directly aii'ect the amount 
of magnetic f^ux which passes through the armature. In 
the series motor, however, the amount of current passing 
through the field coil is directly proportional to the load on 
the motor. Since in a general way the amount of magnetic 
(lux through the armature is proportional to the magnetiz- 
ing power of the field coil, the heavier the load on the motor 
the greater the magnetic fllux, and consequently from equa- 
tion (14) the speed drops on account of greater magnetic 
flux. 




Figure 50 
Diagram of connections of series motor. 



Another thing which causes the speed to drop is the 
voltage lost in the resistance of the field coil and armature. 
Due to these two causes the speed of the series motor is 
exceedingly variable, being high when the load is light and 
the magnetic flux is small, and low when the load is heavy 
and the magnetic flux is great. 



127 

Equation (14) put in another way says that the product 
of the speed and the magnetic flux must always be a con- 
stant quantity as long as the E. M. F. of supply does not 
change. Consequently, when one of these two quantities 
(speed and magnetic flux) is large, the other must be small. 

When constant current is supplied to a series motor the 
speed of the armature will tend to become very high and 
means must be provided for either weakening the field or 
rocking the brushes so as to prevent too great a rise in the 
speed of the armature. 

, The old "Baxter arc motors used the firs.t of these meth- 
ods of controlling the speed, and the Brush arc motors 
used the second. 

The transmission of power by constant current machin- 
ery has been, however, almost entirely abandoned and con- 
stant current arc dynamos are not nearly so much used as 
formerly. The constant potential system having taken its 
place very largely, even for arc lighting. 



QUESTIONS ON CHAPTER X. 

1. What is counter eleotro-motive force? 

2. Is there any difference between the counter electro- 
motive force produced in a motor and the E. M, F. produced 
in a dynamo? 

3. Why will 110 volts force only a few amperes through 
an armature when it is running hjaving* a restist-ance of 1-100 
of an ohm? 

4. How may fhe flux through a motor armature be 
measured by the speed of the armature? 

5. A bi-polar motor armature has 66 slots; each coil 
has thre^ wires; the flux through the armature is 3,600,000 
lines. What will be the speed of the armature on 220 volts? 

6. If the speed of the armature should be 1,050 revolu- 
tions, what would the flux be? 

7. \^%y does the speed of a motor increase as the field 
coils get warm? 

8. Give another instance beside that in the text of the 
identity of ordinary and counter electro-motive force. 

9. What makes the shunt motor constant in speed, 
even under greatly varying loads? , 

10. Why does the speed in a large armature change 
less with change of load than in a small armature? 

11. Why does rocking the brushes to an extreme back- 
ward position raise the speed of a motor? 



129 



12. A two-horse power armature "has a resistance of 
8-100 of an ohm; it is designed to run on 80 volts; one am- 
pere is required to run it at no load; at the heaviest load 
it is designed to take 30 amperes. What would be the drop 
of speed in per cent.? 

13. Why does the speed of a series motor vary so great- 
ly with the load? 

14. Why does the speed of the series motor change so 
much less with the load after the iron becomes saturated? 

15. Why is the speed of a 500-volt shunt motor with 
unsaturated magnetic circu^it almost as high when running, 
on 110 volts as on 500 volts? 

16. How will the speed of a compound wound motor 
vary ? 

17. As long as the magnetic circuit is unsaturated, why 
is the torque of a series motor proportional to the square 
of the current? 

18. To what is the torque of a shunt motor propo- 
tional? 

19. Why does the speed of a series motor tend to be- 
come excessively high? 

20. How is the speed of constant current motors gov- 
erned? 



CHAPTER XI. 



HVSTERESIS AND EDDY CURRENTS. 



When iron is magnetized it tends to retain its magnet- 
ism, and when the directioR of the magnetization is re- 
versed powor is required to affect this reversal. 

Hysteresis may be called molecular friction caused by 
a reversal in positon of the minute molecular magnets of 
which the iron is supposed to be constituted. If the core 
of an electro-magnet should be composed of hard steel fil- 
ings and the direction of current through the magi, izing 
coil should be reversed, it is clear that there would be an 
effort on the part of the steel filings to twist around end 
for end and in doing so there would be more or less fric- 
tion. Something of this same sort takes place when the 
direction of magnetization in a piece of iron takes place. 
It is easy to see that the direction of magnetization in a 
bi-polar motor armature changes twice every revolution. 

An examination of Fig. 31 will show that if the left- 
hand pole be a north pole the magnetic lines will flow 
through the bottom of the teeth on the left-hand side of 
the armatare from the top of the teeth to the bottom, and 
on the right-hand side of the armature from the bottom of 
the teeth to the top. but when the iirmature has made a 
half revolution the direction of tlie magnetic lines will be 
reversed in any particular tooth. 



^v 



131 



Table No. 9 gives Ithe loss in waitts per cubic fokDt at a 
speed of 1,200 revolutions per minute in a bi-polar field with 
various magnetic fluxes per square inch. This table is for 
good soft wrought iron and the hysteresis loss in the iron 
of which ordinary armatures are made, is probably higher 
than that given in the table. 



TABLE No. IX. 



HYSTERESIS IN SOFT IRON. 



Watts wasted per cu. ft. at 1200 

Lines per sq. in revolutions per minute in 

two pole dynamo. 

25,000 78 

30,000 108 

35,000 130 

40,000 155 

45,000 182 

50,000 216 

55,000 238 

60,000 ' 275 

65,000 314 

70,000 348 

75,000 395 

80,000 431 

85,000 472 

90,000 512 

95,000 564 

100,000 620 

105.000 670 

110,000 780 

115,000 964 

120,000 1124 



1 



132 



It will be noted tha^t in a four-pole field the direction 
of magnetization is reversed twice in every revolution, and 
if the armature in a four-pole machine runs at the same 
speed that it does in a two-pole, the loss b^" h^^steresis will 
be twice as great with the four-pole machine as with the 
two-pole. 



EDDY OR FOUCAULT CURRENTS, 



It is clear that there is the same tendency to produce 
current in the iron part of the armature due to the cutting 
of the magnetic lines as there is in the copper wire which 
is wound on its surface. If in Fig. 31 the iron core was 
solid, there w^ould be a very large current circulating in 
the iron core in the same direction as that* which flows 
through the wires in the air gap. Such a current as this 
would be entirely useless and, worse still, w^ould heat the 
armature core very hot; consequently, the armature, in- 
stead of being solid, is built up of thin sheet iron discs. 

These discs carry the magnetic lines without difficulty 
and an armature built up of these discs has the same mag- 
netic properties as a solid wrought iron armature would 
have. 

Fig. 51 shows the direction in which the currents tend 
to circulate around the arm'ature, lajid shows bow these cur- 
rents are prevented from flowing by the insulation between 
the discs. 



L 



133 

The discs in Fig, 51 may be insulated with paper, but 
in practice it is found that the thin coasting- of oxide on 
the outside of each disc is enoug-h to accomplish the same 
purpose and produces an armature which will always re- 
main as solid as when first put up. The use of paper be- 
tween the discs is dangerous, because in time the paper 
charrs and crumbles to pieces, leaving the discs loose. The 
best way to treat the discs is to give them a thin coating of 
linseed oil; this forms a surface having the same insulating 
properties as paper, -and the heat -to whiioh the airmature is 
subjected will not affect it. In practice the discs for arma- 
tures run from ten to twenty-five thousandths of an inch in 
thickness. Even in the thinnest disc there are small eddy 
currents circulating which take power to produce and which 
heat 1he armature core. The loss by eddy currents is 
proportional to the square of the speed at which the arma- 
ture is run, because at double speed, other things being 
equal, the E. M. F. is twice as great, and this double E. M. F. 
pruduces double current. 




Figure 51 

Circulation of eddy currents 

©topped by lamination of the iron. 



134 

Formula S shows that the loss in watts with double 
volts and double current is four times as great as with the 
given voltage. It is because of the loss by eddy currents 
that would occur with solid pole pieces that pole pieces are 
laminated. A consideration of the way in which E. M. F. is 
produced shows that when the number of lines of force en- 
closed b^^ circuit is changed there is an E. M. F. produced 
which tends to send current around the circuit in such a 
direction as to oppose the change. 

When an ironclad armature with a short air gap is re- 
volved the magnetic lines flow from the pole piece into the 
armature in tufts or bunches. These bunches of lines pass 
across the pole piece with the motion of the armature and 
set up currents in the solid pole piece. It is possible by the 
use of a long air gap to cause the lines to flow from the pole 
piece uniforml3\ But with short air gaps it is necessary to 
laminate the pole piece in order to get rid of eddy currents. 
(See Fig. 33). 



QUESTIONS ON CHAPTER XI. 



1. What is ny stereos? 

2. What would be the difference in passing an alternat- 
ing current and a direct current around an iron core as far 
as hysteresis is concerned? 

3. Why is the hysteresis in a four-pole motor itwice as 
great as in a two-pole? 

4. Why is there hysteresis in a revolving armature? 

5. What are eddy currents? 

6. In what (direction would the eddy currents lend to 
flow in the drum armature shown in Fig. 46? 

7. Why is the iron in an armature laminated? 

8. Why are cables used on surface wound armatures 
instead of solid wires? 

9. Why does the pole piece of a motor get warm if an 
iron clad armature is used with too short an air gap? 

10. Why will the heating in such a case be much great- 
er with steel pole pieces than with cast iron? 

11. What will be the loss from the eddy current that 
flows clear around the armature in Fig. 31 if the flux 
through the armature is 1,200,000 lines, the speed of the 
armature is 1,200 revolutions per minute, the resistance of 

the armature between end plates 1-10 of an ohm and the end 
plates are so large as to ihave a megligible resistance? 



136 



12. Is there* any difference in their nature between 
eddy currents and the useful current produced by an arma- 
ture? 

13. Why was paper formerly used between armature 
discs? 

14. Why has this practice been abandoned? 

15. In what way do the watts lost from eddy currents 
vary with the speed? 



CHAPTER Xn. 



ARMATURE REACTION. 




When a dynamo produces current these currents flow 
around the armature in such a direction as to magnetize 
the armature at right angles to the main field magnets. A 
consideration of Fig. 52 shows this, and if the direction of 
circulation of current in Figs. 45 and 46 be worked out, the 
result will be the same. 

The position of the brushes 
on the commutator determines 
irhere the current which flows 
through the armature shall enter 
and leave the armature, and so 
determines the direction of the 
polarity of the armature as an 
electro-magnet. If the brushes 
in Fig. 45 be moved around the 
commutator the point at which 

the current divides to pass around the two halves of the 
Gramme ring will move with it. It is clear that the pole 
of the armature will be at the point at which the current 
divides. The strength of the armature as an electro-magnet 
is directly proportional to the amount of current which is 
dravm from the armature. The practical effect of the arma- 
ture becoming a powerful magnet is to cause more magnetic 
lines to pass into the armature at one side of the pole piece 



Figure 52 

Armature reaction in a 

dynamo. 




138 



than at the other, for a north pole in the armature wilJ 
attract the lines from the south pole of the tield and repel 
those from the north pole. When this action is sufficiently 
great, the axis along which the magnetic lines How is ro- 
tated so as to occupy a position between the polar- 
ity caused by the fields alone and that caused by the arma- 
ture alone. When the brushes are placed as in Fig. 52 mid- 
way between the north and south poles of the Held, the 
only effect of the magnetization 
of the armature is to cause more 
lines to flow into the armature 
from the top of the pole piece 
than from the bo^rtom. The ten^" 
dency is to rotate th'e axis of the 
magnetic lines which pass 

through the armature. It does connter magnetic motive 
not directly tend to decrease the force of armature reaction, 
flux of the lines through the ar- 
mature. As w^ill be seen in the next chapter, it is necessary 
in order to stop sparking in a dynamo to 
rotate the brushes a short distance in the 
direction of the rofaficm of the armature. This 
produces the oomdition of things shown in Fig. 53, in which 
the armature reaction is such as to directly oppose to some 
extent the passage of the magnetic flux through the arma- 
ture. It will be seen that if the brushes were rotated sl/il 
further forward that the magnetism in the armature would 
still further oppose that of the fields. In arc dynamos the 
armature is made relatively a very powerful magnet and 
its magnetizing action is fully equal that of the fields. By 
rotating the brushes it is easy to see that the amount of 
magnetic flux which would pass through the armature could 
be very greatly altered. In the Wood arc dynamo the regu- 



139 

lation is entirely effected in this way. In the Brush arc 
dynamo part of the current is shunted by or around the 
ield coils; this makes the armature relatively much strong 
er than the fields, and the armature reaction prevents mag- 
netic flux from flowing through the armature, as will be 
more fully explained in the chapter on sparking. 

When the field is relatively weak, with reference to the 
armature, it is necessary to rotate the brushes through a 
considerable arc in order to stop sparking; the rotation of 
brushes makes the effect of the armature reaction much 
greater than it otherwise would be. In fact, if the brushes 
of a Brush arc dynamo be always rotated to such a position 
that the spark is the same length, it is necessary to reduce 
the current in the fields only from 9% to 7 amperes, to re- 
duce the flux through the armature from a maximum to 
zero. The armature reaction with 10 amperes is equal in 
magnetizing force and opposite to that of the fields with 7 
amperes. 

If the brushes of a series dynamo be rocked quite well 
forward in the direction of rotation and current be sent 
throjjgh the armature alone, the magnetizing force of the 
armature will set up a powerful magnetizing flux through 
the armature and fields; and, if the machine be run as a 
motor, it will operaite as if Itlhe field coils were in ^(dtdlon, 
with the exception that it will spark furiously. In this 
case the armature reaction furnishes the magnetic field. 

In ordinary constant potential dynamos and motors the 
armature reaction is a necessary evil, and the dynamo should 
be carefully designed so that the armature m'agnetizing 
force shall never reacih more than from 1-2 to 2-3 the mag- 



140 



netizing power of the fields. That is, th€ ampere turns on 
the armature a-t full load should be from 1-2 to 2-3 the am- 
pere turns on the field at full load. 

As was noticed in Chapter IX, there are twice as many 
turns of wire required on a Gramme ring airm-ature as on a 
drum armature 'to produce the .same number of conduc- 
tors, in which the E. M. F. is set up by means of the rota- 
tion of the armature; that is, the same number of amperes 
produce twice as many aonpere turns in a Gramme ring 
armature as in a drum armature of the same power. This 




Figure 54 
Flow of current in multipolar dynamo. 



© Indicates current flowing toward the observer. 
X Indicates current flowing away fvQm the observer. 



141 

fact make the Gramme ring a superior armature [Por arc 
dynamos ^vhere it is desired to have the armature a pow- 
erful mag*nat, -and indicates that the drum armature is the 
better armature for coaistant potential dynamos in which 
the armature reaction is to be avoided as much a'S possible. 
It is to red'uce the effect of armature reaction that large 
eonsitant potential dynamos are made multi-polar. 

Fig. 54 is the diagram of a six-pole dynamo with a 
drum armature, and shows the direction in which the cur- 
rents in the armature flow. It will be seen that the number 
of turns under each pole may be made quite small, but that 
the number of ampe-re turns required on the fields will be 
larger on the multi-polar machine than on the bi-polar, be- 
cause the area of the aiir gap is relatively much smaller. 
The small number of turns on the anmature and the larg^e 
number of ampere turns required on the field make it pos- 
sible for the armature to carry very heavy currents, withooit 
allowing the number of ampere turns in the armature un- 
der each pole to become great enough to seriously distort 
the field. 



QUESTIONS OiX CHAPTER XII. 

1. \Miat is armature reaction? 

2. On -svhat does the strength of the armature as a 
magnet depend? 

3. In what way is the armature magnetized with ref- 
erence to its field? 

4. Why is the pole piece which the armature is leav- 
ing in a d^maono magnetized more strongh^ than Ihe appo- 
site one? 

5. Why does -tJie movement of fthe brushes affect the 
armature reaction? 

6. Why does armature reaction usually reduce the 
amount of flux? 

7. Hmv would the brushes have to be set in a dynamo 
to increase ithe amount of flux through the armature? 

8. In What kind of djmamos is it desirable (to have ar- 
mature reaction? 

9. How is the regulation of the Wood arc dyna/mo 
efilected? 

10. How is the regulation of a Brush arc d3Tiamo ef- 
fected? 

11. How sbocld the brushejs on a motor be set in order 
to dispense witii the field coil? 

12. In donstant potential machinery, how strong is it 
best to make the magnetizing power of the armature at 
full load with reference to the fields? 



143 

13. Why is the Gramme ring- anexcellemi form of af- 
m^ature fo-r sl constant .current machine and a poor form for 
a (Constant potentda.l machine as compared with a drum 
armature? 

14. What device is used to prevent the effect of arma- 
ture reaction dn larg-e machines? 

15. With the same mumber of turns on the armature, 
how mueh will the .armature reaotio^n be reduced by chang- 
ing- from two to four pole? 



CHAPTER XIII. 



SPARKING. 



Intimately connected with armature reaction is the 
sparking* that occurs on the commutator of the direct cur- 
rent dynamo or motor." Every ordinary machine 
has a load -at which it will spark. Consid- 
eration of Fig-. 55 shows that the current is 
flowing through the coil in one direction just before 
it reaches the brush and is flowing through it in the oppo- 
site direction just after it leaves the brush. During the 
ome that the ooil is short circuited by the brush, the direc 
tion of the current is completely reversed. Fig. 55 shows 




o^ — ^-^o 

Figure 55 
Commutation in Gramme ring armature. 



this in detail. Three coils are shown, a, b and c. In c 
the current is traveling through the coil in one direction; 
/he coil b is short circuited by the brush. In c the curren: 
ife traveling through the coil in the opposite direction tc 
ihaX in a. 



145 

The currents in coils c and a are eaoh equal ito half the 
total armature current. The current in the short circuited 
coil will depend on the magnetic field in which 
it is moving' while it is short oircurted. If 
it is still under the icafluence of the north 
pole which it is leaving, the current will immediaitely 
increase as soon as it is short circuited by the brush, and 
may continue quite large until it is about to leave the brush. 
Then the resistance in its circuit, due to the small surface 
of the brush which rests on the commutator bar, reduces 
it to zero. A ourrent must nofw in a very small space of 
time increase in the coil b from zero to the full value of 
half the armature current. The self-induction of the coil b 
prevents this from being done and the commuitator bar c, 
leaves the brush before the current in coil b has reached its 
full value. A short arc is now formed between tihe extremity 
of the brush and the bar c, which lasts until the electro- 
motive force has overcome the self-induction of the coil b 
and raised the current in it to half the armature current. 
It should be explained here that the self-induction of a coil 
is of the same nature as inertia in a weight. The inertia 
tends to prevent motion from being imparted to the weight, 
but when once in motion the inertia tends to prevent the 
weight from coming to rest. 

The self-induction in a coil acts the same way with ref- 
erence to the electric current. It tends to prevent the cur- 
rent from being established in the coil, but, when once es- 
tablished, tends to prevent it from changing value or from 
dying out. 

The self-induction of a coil surrounding an iron core is 
very much greater than that of t^e same coil in the air; 
furthermore, the self-induction of a coil increases as the 
square of the number of turns in the coil. 



146 



We have traced the actiooi in the eommutaftion of the 
call b where the brush is rocked so far back in the direc- 
tion opposite to thait of rotaitfiom that the coil b is still cut- 
ting- the lines whion flow from the pole which it is leaving. 
Under these circumstances it is seen that the self-induction 
of the coil prevents the current from being reversed until 
so late that a small arc forms between the point of the 
commurtator brush a-nd one oif the commutato-r bars to 
which it is attached. This continual arcing is called spark- 
ing. When, however, the brush is rocked forward in the 
direction of rotation until the' coil b is cutting the lines of 
force which flow from the pole which it is 'approaching, 
the action is very different. Fig. 56 shows the relative 
position of the poles and the coil being commutated. 

When the brushes are rocked into the position shown in 
Fig. 56 the coil b is short circuited while it is cutting lines 
from the south pole, or the pole toward which it is ap- 
proaching. The E. M. F. generated in the coil b will be op- 
posite to that generated 
while the coil was under 
the influence of the north 
pole; therefore, as soon as 
the coil b is shortcircuited 
by the brush theE.M.F.set 
up therein tends to reduce 
the current in the coil to 
zero and next to generate 
a current In the coil to the 
reverse direction. J-f all the 
conditions are just right 

this current will be equal to half the armature current at 
the moment the bar c' leaves the brush. When these con- 




Figure 56 

Diagram of correct and sparkless 

commutation. 



147 

ditions obtain, there is no possibility of any arcing between 
the commutator bars and the brush, and consequently the 
commutation is sparkless. It is necessary that the coil b 
should be in a field which will not tend to increase the 
current that is already flowing in it at the moment that the 
coil is first short circuited. It is clear that the exact con- 
ditions which would make sparkless commutation possible 
if sparkless commutation depended only upon magnetic con- 
ditions can only exist for one particular position of the 
brushes and one particular load on the armature. For, sup- 
pose the coil b were short circuited in a quite powerful field 
of the pole toward which it is approaching, then a current 
flowing in it at the instant it was first short circuited would 
die out almost immediately and a large current would be 
sat up in the opposite dia-ecftion, amd would 'tend to increase 
until broken by the bar c, leaving the brush. This would 
produce an aire due to OA^er-eommutaltion. 

A factor of very great importance in commutaition 
is the resistance between the brush and the commutator 
baj's. It must be carefully kept in mind that while the 
current in the coil b is being reversed by the small E. M. F. 
generated in it, the main current of the dynamo is passing 
from the co.mmut:.ator bars b, and c, to the brush. There 
will therefore be a greater or less difference of potential 
between the bars b, and c, and the brush. This difference 
of potential or voltage will depend on the resistance be- 
tween the brAsh and commutator bars and also upon the 
current. It is clear that if there should be a tendency in 
the coil b to over-commutate by being placed in too strong 
a south field, this local current must flow through the leads 
c„ and b„ across from the bar b, through the brush to the 
bar c, and to the doil. In order to do this the current which 



148 

naturally flows from the bar b' into "the armatncre will be 
increased. While the current which naturally runs from 
the brush through the lead or connection c" to the arma- 
ture is reduced by the same quantity. This consideration 
w'M show that there is very little danger of over-commuta- 
tion when the armature carries a fairly large load. 

The tendency of a considerable armature current trav- 
eling from the brush into the bars and so into the armature 
is to immediately stop any current which might flow in 
the coil b, because the tendency is for the leads or connec- 
tions c" b" to carry the same amount of current. And 
this tendency is increased if there is considerable resistance 
in the two leads c" and b". When these two leads are 
carrjdng the same amount of current it is manifestly im- 
possible for any local current to circulate in the coil b. As 
the bar c' moves away from the brush the resistance thait 
the current meets in flowing from the bar c' increases on 
account of the smaller surface of contact between the brush 
and the commutator bar c'. This tends to reduce the cur- 
rent in the lead c", but such a reduction of the current 
must be accompanied by a corresponding increase of the 
current in the coil b. 

This is becauise )the current m. the doiil ib p'lus the current 
in The lead c" must -always equ«al h<alf the arma)ture current, 
and anything that reduces the current through the lead c'' 
must increase the current through the coil b. 

The resistance between the brush and the commutator 
bar c' thus powerfully tends to set up a current in the short 
circuited coil in the same direction that it will flow in the 
coil after it is completely commutated, because it tends to 



149 

produce an even dis.tril3ution of current over the surface of 
the brush. 

As the har c* irecedes from the brusih the reslsitance to 
the passage of current to the left hand side of the armature 
by the path c' and c" increases, and ithis increases the ten- 
dency of the current to flow through the coil b. When the 
bar c' has entirely left the hrush the current in the coil b 
will be equal to half the armature current, and in this way 
again sparkless commutation will have been attained. 

If the brush is of carbon instead of copper, the resist- 
ance between the bar and the brush will be very much 
greater with brushes of the same size. But even with a car- 
bon brush large enough to carry the current there will be 
from three to five times the voltage between the commu- 
tator bars and the brush that exists with a copper brush. 

A still more important factor in sparkless 
commutation is i-he more even distribution of 
current between the brush and commutator bars 
that the carbon brush imposes. The resistance of the car- 
bon is at least 100 times as great as that of a block of cop- 
per the same size, and therefore the tendency of the cur- 
rent to spread itself out evenly over the surface of the brush 
when passing from the commutator bars to the brush is 
very great. If this effect is great enough when the brush 
<«overs bath commutator bars b' and c', fully 25 amperes will 
flow from each commutator bar to the brush, provided the 
armature is carrying 50 amperes (see Fig. 57). When the 
commutator bar c' has advanced so that only half its surface 
is covered by the brush, 121/3 amperes flow into the brush 
from the coramu»ta.tor bar c' 25 a-mperes from the commuta- 
tor b', and 12yo amperes from the commu-tator bar a', which 



150 



would by this lime have half its surface covered by the 
brush (see Fig*. 58.) ^At (this instant the coil b would be 
carrying 12i/$ amperes into the left hand side of the arma- 
ture and would be, so to speak, three-quarters commutated. 
The coil a would be carrying 12l^ amperes into the right 
hand side of the armature and would be, so to speak, one- 
quanter commutated. As the commutator bar c' leaves the 
brush the current flowing from the brush into the commu- 
taitor bar c' will diminish until at the instant the bar 
leaves the brush it will be zero, and the current in the coil 
b will correspondingly increase until, at the instant the 
commutator bar c' leaves the brush, it will be equal ito full 25 
amperes, or one-half the armature current. At this instant 




Figure 57 
Current from armature 50 amperes. Current into bar e', 25 am- 
peres and into bar b', 25 amperes. Current through both 
c" and b", 25 amperes leach. Current in coil b, 
none. Current in coils a and c , 25 amperes each. 



the brush would rest equally on the baTs a' and b', 25 am- 
peres would flow into each bar, 25 amperes would flow into 
each lead a'* and b" and the current in the coil a w^ould be 
Induced to zero, or it would be half commutated (see Fig. 
59.) 

The objection to the copper brush is that the resistance 
between the copper brush and the commutator is so low 



151 



that the current can easily bunch up on one side of the 
brush; for instance, when the commu'tator bar c' had moved 
to such a position that only one-third of its 'surface rested 
under the brush, the resistance of contact would be so low 
that the 25 amperes of armature current could easily flow 
into it. If this should be the case the current in the coil b 
would have to be built up almost instantly and a large cur- 
rent would flow from the tip of the brush into the com- 
mutator bar c' jast as the bar was leaving- the brush. 
Enough current would flow, in fact, to fuse the very tip of 
the brush and bar at the edge of the bar, 
and the fused bit of copper would appear 
as copper dust thrown off from the commu- 
tator. This fusing action roughens the bars, whioh tends 




Figure 58 

Current from armature 50 amperes. Brush covers half bar c' 

all of b' and half of a'. Current into bar c', 123^ amperes. 

Current into bar b', 25 amperes. Current into bar 

a', 123^ amperes. Current through coil b, 

12j^ amperes. Current through coil 

a, 123^ amperes. 



to make commutation still more imperfect. Trouble of this 
kind once started grows rapidly worse, until it is necessary 
to put on new brushes or to retrim them and to true up the 
commutator. The higher resistance of carbon makes it 
impossible for enough current to pass from the edge of the 



152 

copper bar to the tip of the carbon brush to fuse the copper. 
The action just described, viz: the distribution 
of the current over the surface of the brush 
is the most important one in the progress of 
commutation. The only thing which prevents this 
from always producing spairkless commutation is {the self- 
induction of the coil to be commutated. It is clear that if 
commutation is to take place easily this self-induction 
should be as low as possible. If three-tenths of a volt ap- 
plied for 1-100 of a second is sufficient to overcome the self- 
induction of a coil of one turn on a given armature, 1 2-10 
volts, or four times as much as would be required to over- 
come the self-induction and reverse the current in a coil of 
two turns on the same armature. Nine times 3-10 would be 




Figure 59 

Current from armature 50 amperes. Brush covers all bars 

a' and b'. Current into bars a' and b', 25 amperes each 

Current in coil a=0. Current in coil h=25 

amperes. Coil b completely commutated. 

required with three turns, and so on, for the self-induction 
of a coil on any given armature is proprtional to the square 
of the number of turns on the armature coil. 

It will be noticed that the effort to commutate the 
short circuited coil due to the resistance of the brush in- 



153 

creases with heavy loads; thus there is twice as much teai- 
dency for the current to flow in<to the brush evenly with 50 
amperes as there is with 25. This gives us twice the 
voltage for commutating the current in a sihort circuited 
coil when 50 amperes are flowing than is available when a 
current of 25 amperes is being produced by the armature. 
On the other hand, the commutation which is prioduced by 
the short circuited coil cutting the lines of the fleld toward 
which it is approaching, grows weaker a.nd leas perfect as 
the load increases, because the in creasing load increases 
the armature reaction and the increased armature reaction 
weakens the field which the coil is approaching, w:hile 
strengthening the pole from which -the coil is receding. 
Therefore the commutation produced by the cutting of 
lines of foiX3e is strongest when it should be weakest and 
weakest when it sho-uld be strongest. Since perfect com- 
mutation is obtained even under the most trying conditions 
it is clear therefore that it is produced mainly by the ten- 
dency to the even distribution of the current on the brush, 
and not to the character of the fielcl in which the short cir- 
cuited coil is moving. In order to obtain the best results, 
or even good results, it is necessa-ry tha't the coil while 
short circuited should not be bo any extent under the mag- 
netic influence o'f the pole from whidh it is receding. We 
may therefore sum up the requirements to good commuta- 
tion as follows: First, cairbon brushes of suificiemt width 
to give the coil time to reverse; second, low self-induction 
of the short circuited coil, so that only a small E. M. F. 
need be applied in order to reverse the current in it; third, 
an armature in which the reacitdon is sufficiently small, so 
that the pole tow^ard which the short circuited coil is ap- 
proaching is noit very much weaker with the heaviest load 
than with no load. 



154 



The above description applies to the commutation in a 
dynamo. The same description will apply to the. commu- 
tation in a motor, except that in order to obtain magnetic 
reversal of the coil the brushes muisit be rocked in a direc- 
tion opposite to that of rotation so as to bring the short 
circuited coil under the influence of the pole which the 
short circuited coil is leaving instead of approaching, as in 
the case of the dynamo. 

A little thought will show that in the case of both dy- 
namo and motor it is necessarj% in order to produce mag- 
netic commutation, to have the short circuited coil under 
the influence of the pole that is weakened by the armature 
reaction. 

Figs. No. 57, 58 and 59 show in three steps the process 
of commutation in coils a and b. 



QCJESTIOXS ON CHAPTER XIII. 



1. 'What happens to the direction of flow of current in 
a coil in passing" a commutator brush? 

2. In a bi-polar armature how much current is passing 
through each coil? 

3. On whait dioes ^the current lin tbe aoil tor colils sih'0<rt 
circuited hj the brush depend? 

4. What is the effect of introducing resistance in the 
leads between the armature windii>.g and the commutator 
bar? 

5. What is the condition of sparldess commutation? 

6. What is the effect of self-induction in a coil? 

7. How much sparking would there be if self4nduction 
could be entirely eliminated? 

8. Why is the sparking less in a dynamo and greater 
in a motor when the brushes are rocked forward in the 
direction of rotation? 

9. If nothing but magnetic conditions govern sparking, 
would it be possible to obtain perfect commutation under 
all loads? 

10. What is over-commutation? 

11. How would you set the brushes of a dynamo so 
that it would spark less with a load than without a load? 

12. 'What other important factor is to be considered in 
commutation? 



156 

13. What is the effect of difference of potential be- 
tween the brush and commutator bars in commutation? 

14. Why is over-commutation very unlikely to occur 
with considerable load on the armature? 

15. Wh}^ do carbon brushes prevent sparking? 

16. Why does the commutator run warmer with car- 
bon than with copper brushes? 

17. If means could be devised to cause the current to 
pass evenly from the brush 'into the commutator, what 
effect would this have on sparking? 

18. Why does the carbon brush approximate this con- 
dition more closely than the copper brush? 

19. Whj^ does a brush whic'h covers two or three com- 
mutator bars work with less sparking than one whioh is 
very narrow? 

20. Describe the action of a carbon brush in producing 
commutation. 

21. Whj^ is sparking usually accompanied by cutting 
of the commutator? 

22. If it is necessary to use a copper brush, whait must 
be true of the self-induction of the coils? 

23. What does the fact that motors may be run heavily 
Joaded in both directions withouit •sparking sihiow as to tihe 
relative importance of the magnetic conditions and the 
brush design in producing sparkless commutation? 



CHAPTER XIV. 



WINDING OF DYNAMOS AND MOTOHS, 



The office of the wire on an electric dynamo or motor 
is twofold: First, wire is used on the magnetizing coils to 
convey the current which causes the iron or steel cores to 
become electro-magnets. This winding should simply be 
disposed and connected up so as to force the magnetic flux 
around the circuit. If possible, it is always better to wind 
the magnetizing coil in the shape of a cylinder, for a circle 
includes the largest possible area with the smallest possible 
periphery. It is, of course, the object of the magnetizing 
coil to driA^e as many lines of force as possible through its 
interior; at the same time it is very desirable that the length 
of the average turn of the field wire should be as small as 
possible. Therefore it is always advisable to make the 
cross-sections of that part of the magnetic crrcuit around 
which the magnetizing coil is placed a circle or a square 
with the corners cut of¥, or, if a laminated pole piece is used, 
a square. The field v^inding should also be placed as close 
as possible to the air gap. This is to prevent as far as pos- 
sible magnetic leakage. 

The second object of the wire on an electric dynamo or 
motor is to carry the current which passes through the 
armature. We will consider simply the case of the dynamo, 
for, as was pointed out in the chapter on *'Electro-Motive 
Force," a d3^namo and motor are perfectly similar machines. 



153 



and one may be converted into the other without the knowl- 
edge of an observer watching the machine in operation. 

In the case of the dynamo, p]. M. F, is generated in the 
armature wires as they pass under the pole piece. An equal 
amount of E. M. F. is generated in each wire, and in order 
to get the best result these wires must be connected up into 
a series, so that all the electro-motive forces generated un- 
der a field pole shall be added together. 

When the winding is arranged so that this is accom- 
plished, the current will flow* in all the wires under each 
pole piece in the same direction. Since the E. M. F. pro- 
duced under the north pole is opposite in direction to that 
produced under the south pole, it is further necessary to 
arrange the winding so that the current in all the wires 
under the north pole shall flow in one direction and the 
current in all the wires under an adjacent south pole shall 
flow in the opposite direction. 

A study of Figs. 45, 46 and 21 will make this clearer. 
Any armature winding w^hich fulfills the above conditions 
will operate satisfactorily. Fig. 60 is a diagram of the 
winding on a two-pole drum armature. Here the end of 
one coil and the beginning of the next coil are brought 
down and atitaehed to a commuitator segment. Suppose 56 
coils are used on the armaiture and 56 bars in the commuta- 
tor, 'and four turns on each coil, and that tlhe armature is 
of such diameter as to accommodate 56x4 equals 324 wires 
in a single layer. By the time 28 wires or lead's are brought 
down to the commutator the whole surface will have 
been covered with -a layer of wires. In order Ito bring down 
enough connections to fill up the other half of Jtlhe commu- 
tator, it will be necessary to wind on a second layer 



159 



of Wires over the firs>t layer. Now between any 
two ordinary coils in eit-her layer of the armature 
winding there will be only the. diffe.rence of poten- 
tial or voltage that exists between two adjacent bars 
in the commutator. When the last coil is wound onto the 
first layer it will be seen that it lies alongside of the first 
coil that was put on, so that between the first and last coils 
that are put onto the layer of the armature we have the 




Figure 60 

Diagram of connection of bipolar armature, 

horizontal winding. 



160 



full voltage which the armature is designed t(3 carry. There- 
fore, while it is not necessary to insulate between adjacent 
coils in the same layer, it is necessary to carefully insulate 
between the first and last coils that go on the same layer, 

A study -of Fig. 60 will furthermore show that there is 
in eYery part of the armature the-full difference of poten- 
tial of the armature between the upper and lower layers 
of wires. Therefore it is necessary to insulate very care- 
fully the upper and lower layers. A winding such as is 
shown in Fig. 60 is called a horizontal winding. If, instead 
of winding the four turns of each coil alongside each other 
in one layer, they should be wound with two turns in two 
layers a space would be left between the coils which are 
attached to adjacent bars on the commutator. This space 
may be filled by winding in a coil w^hich is connected to a 
bar on the opposite side of the commutator. 

Fig. 61 shows a diagram of this 
winding. It is to be seen that each 
coil must be insulated from its neigh- 
bor for the full difference of poten- 
tial in the armture. This is called a 
vertical winding. Practically, a hori- 
zontal winding is less liable to trouble 
than the vertical winding, because it is 
easier to insulate the layers from each 
other than it is the vertical divisions 
between adjacent coils. 

It is possible to carry the leads 
connecting the armature winding and 
the commutator bars a quarter revolu- 
tion more or less around the armature if desired, 
in order to bring the position of the brushes into a more 




Iqo 

Figure 61 

Diagram of vertical 

winding for bipolar 

drum armature. 



\ 



161 



convenient location than they would have if the leads were 
brought out straight as shown in Figs. 60 and 61. 

In a four-pole machine iwo general methods of winding 
may be pursued, one is called a wave winding, the other a 
lap winding. In the wave winding there are only two paths 
for the current through the armature, and the current in 
passing from one commutator bar to the next is compelled 
to flow under all the poles on the dynamo. This is shown 
in Fig. 62. With a wave winding either tvro or four brushes 
may be used. This method of winding possesses the great 
advantage that the E. M. F. produced in each of the two 
paths in the armature must necessarily be equal, even if 
the magnetic flux from the poles is very unequal. 

The diagram shows for convenience of representation 
a eommnrtator «with onllv nine 'bars. 




Figure 62 
Wave winding on four pole dynamo. 



l«g 



The brushes in a four-pole dynamo are placed 90 degrees 
apart, in a six-pole dynamo CO degrees apart on the com- 
mutator. In a four-pole dynamo brushes opposite each 
other should be connected together. In a six-pole dynamo 
three sets of brushes 120 degrees apart should be connected 
together to one pole or terminal of the dynamo. 

Another advantage of the wave winding as compared 
with the lap winding for small machines is that the number 
of turns of wire on the armature is half as great with the 
wave winding as with the lap winding. 

When one is calculating the voltage w-hich will be pro- 
duced in a four-pole dynamo on w^hich a wave winding is 
to be employed, it is necessary to have flux enough from 
each pole to produce only half the total voltage required. 



I 



w — > 




Figure 63 
Lap winding on four pole dynamo 



163 



Tills is on account of tlie fact that there are only two 
paths for the armature current. 

The lap winding* shown in Fig. 63 is perfectly analogous 
to the winding shown in Figs. 60 anu 61. In this machine 
there are four paths for the current through the windings 
of the armature, and the connections, instead of being com- 
plicated as with the wave winding, are as simple as with 
the Iwo-pole winding. By cross connecting opposite bars 
of the commutator it is possible to use either two or four 
brushes on a four-pole armature with a lap winding. In 
the wave winding the commutator bars are cross connected 
by the armature wires themselves. 

In the lap winding there are four paths for the a.rma- 
ture current through the armature. There must neces- 
sarily be four brushes on the commutator, unless the 
commutator is cross connected, and the voltage produced 
in each of the four circuits depends on the magnetic flux of 
its respective pair of poles. 

It may happen in this way, that after the armature has 
worn the bearings so as to be out of center in the fields 
that the E. M. F. in one circuit may be considerably higher 
than that in the circuit on the opposite side of the arma- 
ture. 

In a bi-polar machine the two sides of the coil must 
fpan nearly or quite 180 degrees of the armature in order 
that one side of each coil may be under a north pole while 
the other is under a south pole. In a four-pole machine 
each armature coil must span nearly or quite 90 degrees 
for the same reason. In a six-pole machine a span in each 
coil of 60 degrees is required. ' 



^ 



^ 



164 



One peculiar thing is noticed in a wave winding* on a 
four-pole machine, when there are about half as many slots 
in the armature as there are bars in the commutator. One 
coil cannot be connected to the commutator and must be 
taped up and left in the armature without any electrical 
connection with the rest of the armature winding. Tap- 
ing up this coil makes the number of bars in the commu- 
tator one less than twice the number of slots in the arma- 
ture. Table No. 10 gives the arm.ature windings and the size 
of the wire required for a number of the armatures most 
commonly used in the United States. 



165 



fJ 



TABLE No. X, 



EDISON GENERATOR WINDING. 







o 






















Ui 


<M 






Kind 
of 


o 






a; 
2So 




U CO 


0) 


u 


Winding 


% 


£2 


5- >» 




i? 


* ri 

Q^ 




N 


1 


!3 eg 


«3 % 


^ 0) 


O 




.072 


Hh^ 


>AXi 


JZiOQ 


^ 


3 


Horizontal 


3 


2 


44 


125 


6 


♦' 


.050 


2 


2 


3 


58 


250 


12 


Vertical 


.148 


1 




3 


50 


125 


15 


«t 


.180 


1 




2 


48 


125 


20 


(( 


.110 


4 




2 


40 


125 


20 


Horizontal 


.083 


6 




2 


66 


125 


25 


»( 


.162 


2 




1 


66 


125 


30 


»( 


.195 


2 




1 


58 


125 


45 


i( 


.083 


3 




2 


100 


500 


60 


Vertical 


.134 


2 




3 


58 


500 


100 


(i 


.120 


4 




2 


80 


500 





^ 




i— ( 




P 




^ 




^_« 




^ 




e 




^\J 






3 


H 


G 


<^ 


1 


S 


8 

1 




1 


p^ 


'A 


c 


. 


H 


o 


c 




>H 


pq 


< 


< 


b^ 


H 


^ 



H 



w 


ui 


G 


o 


£t»£ 


03 


^ c 




o^ 


--J 


s§ 


a 


cl^ 


c 


o 


o 


O 


O 



u^dg siToo 



spuBajaAo 



9-1 TAV JO 9ZTS 



uoijoag 

JO SITOQ 

jaqran^ 



SnrpuTAV 
jopuhi 



8JO0 

}o puT:a 



M 



O O t-c 
4J -t-^ -<-> 

CJOOOOQ 












a 
o 

bCo 

I- 



c3- 3 



oooo* 



fi G p; !=! 

08 ca c3 c3 



»ft CC 1-1 kft -^ «o OS 
C^ r1 rl CM 11 C^J 

TD XJ 'O 'd 'O TU 'U 

c c2 f: c c c c 

ce C3 d cj si c3 ci 



5^S 2 

' O O . ^ '^ '^. ^ '^ '^ ". '^ '^. '^e '-^. ^. 



•^•^-^■^-<*O»ftCCirtt-(M»ftCCC0»fti-H0iCC<:DO 

cococTcocDcooosocct'Ososososifrcicciftcvj 



73 

c3- 



. go.. 



-if '^^ 

O- ^ +J- - 






02 OQ 



cc^i 



0:h* 




'd 

(V 
ft 
>* 

u 
> 

O 

> 

o 

83 

c3 
> 
"So 

en 
bO 



167 



1 



TABLE No. X.-Oontinued. 



WINDINGS OF ARC- ARMATURES. 



^r 


1- 


o 




ber 
rs per 
on 


,0 CC tH 


^u 


Armature 


t^ 


0) 


.§'-^ 


^X?. 


S£g^ 






ee^ 




B S 


^ 03 g 


S :3 * 


03 o 




Oh^ 


s 


^^ 


"AyAm 


52;hh; 


Ofl. 


Brush No. 7 


30 


.083 


8 


17 


36 


2000 


Brush No. 8 


65 


.083 


12 


21 


30 


2000 


Brush No. 9 


85 


.083 


24 


23 


19 


2000 


Brush No. 10 


100 


.083 


24 


23 


21 


2000 


Brush No 11 


125 


.083 


24 


22 


24 


2000 


T. H. Rinff M. D. 
Schuyler 


50 


.072 


30 


15 


11 


2000 


50 


.057 


8 


8 


37 


1200 


Wood No. 8 


60 


.064 


120 


11 


6 


1200 


Wood No. 9 


80 


.072 


120 


13 


6 


1200 



168 



COMPOUNDING OF DYNAMOS. 

We have considered heretofore two general methods of 
field winding, viz: shunt and series. A combination of 
these two methods is called compound winding. In a shunt 
wound dynamo the excitation is almost constant, but the 
voltage produced by the dynamo decreases as the load in- 
creases, due to four causes: First, in order to obtain 
sparkless commutation the brushes are rocked forward into 
suoh a position that the coil, while short circuited by the 
brush, is under the influence of the pole toward which it is 
approaching. The armature reaction with the brushes in 
this position decreases the magnetic flux. This lowers the 
voltage. Second, the armature reaction tends to bunch the 
lines very greatly under one side of the pole 
and to thin them out under the other s:ide 
of the pole. In a surface wound armature this action 
does not greatly alter the total magnetic flux, but when an 
ironclnd armature is employed the armature teeth are satu- 
rated by the action of the normal field, and the effect of the 
armature reaction cannot greatly increase the flux of the 
lines under the dense end of the pole piece. Consequently 
all the lines which are prevented from passing into the ar- 
mature at the other end of the pole piece practically dimin- 
ish the total magnetic flux by just this amount. Third, 
the current flowing through the shunt fields is decreased, 
owing to the loss of voltage produced Tn the armature by 
the efFect of the armature reaction. Fourth, a rea- 
son which in large armatures is of practically little import- 
ance is the loss of voltage due to the resistance of the arma- 
ture. The combined effect of these actions is to reduce the 
voltage from 5 to 25 per cent, between no load and full load. 



169 



II is desirable, of course, that the dynamo produce at the 
lamps a perfectly constant voltage. To satisfy this condi- 
tion the voltage at the dynamo at full load must be greater 
than the voltage at no load by the amount of the loss of 
voltage in the line. In order to accomplish this result and 
counteract the effect of armature reaction, a series v^inding 
is put on to the fields of the d^^namo. The effect of this 
series winding is to increase the ampere turns on the field 
coils in proportion to the load. Therefore, when the arma- 
ture reaction tends to reduce the voltage by the greatest 
amount the series coils tend to increase the voltage to the 
greatest extent. By using the proper number of series 
turns the effect of armature reaction can be overcome and 
the voltage increased as the load increases, thus making up 




x-x-x-x-x-J 

Figure 64 • 
Diagram of compound winding in a dynamo. 



170 



for line loss. Fig. 64 is the diagram of compound winding 
on a dynamo. Fig. 65 shows the effect of the series coil. 

Compound winding can be used on motors as well as 
dynamos. The effect here is to increase the torque and 
decrease the speed of the motor as the load increases. A 
little thought and a consideration of Fig. 20 will show that 
the torque or twisting effort is proportional to the current 



^90 



i60 



JZe 



to 



-10 











__________^ 


n 








^ 


J 








--\ 










N 










AMPERES 



;ioo 



300 



400 



5— 



Figure 65 



Upper line shows the current and voltage when series coil is used. 

Lower line shows current and voltage when plain 

shunt winding is employed. 



which flows through an armature as long as the field is 
constant, and is always proportional to the product of the 
current through the armature and the strength of the field. 
An advantage of compound wound motors is that the speed 
variations which will occur when a plain series wound motor 
is used are confined within definite limits. At the same 
time the advantages o/ the series motor are obtained, viz: 
First, powerful starting torque; second, the decreased effect 



171 



of armature reaction, which shows itself in freedom from 
sparking at heavy loads. In calculating the number of am- 
pere turns required on a compound wound dynamo, it is 
necessary to calculate the number of ampere turns that 
would be required to force five or ten per cent, additional 
flux through the circuit. 

The effect of the shunt coils is usually sufficient in an 
ironclad armature to saturate to a considerable extent parts 
of the magnetic circuit. This makes it necessary that the 
ampere turns of the series coil should be much greater than 
would otherwise be necessary. 

In practice the ampere turns of a series coil at full load 
vary from one-third to one-half the ampere turns of the 
shunt coil. 



QUESTIONS ON CHAPTER XIV. 



1. For what two purposes is wire used on a dynamo 
or motor? 

2. Why is it desirable to make the section of the field 
coil circular? 

3. What advantage is gained by placing the field coil 
near the air gap? 

4. In order to have a motor winding properly arranged, 
w^hat must be the direction of the current in all the wires 
under each pole piece? 

5. Why does the coil winding on a four-pole dynamo 
span one-quarter of the circumference of the armature? 

6. How many degrees will a coil span in an armature 
intended for a ten-pole machine? Why? 

7. Why is it necessary for the current in all the wires 
under the north pole of a motor to flow in one direction and 
in the opposite direction under the adjacent pole? 

8. AMiat is the difference of potential between the first 
and last coils in the same layer of a two-pole, two-layer 
horizontally wound armature intended for 500 volts? 

9. If the armature has 64 sections, what would be the 
difference of potential between the third ^pd fourth coils? 
Eleventh and twelfth? 



173 



10. In the same armature, wliat would be the differ- 
ence of potenftial between the upper and lower layers of 
wire? 

11. What is a horizontally wound armature? 

12. What is a vertically wound armature? 

13. How is it possible to connect the armature to the 
commu'tator so as to have the brushes set in any desired 
position? 

14. 'VMiat is a wave winding? What is a lap winding? 

15. What are the advantages of wave winding for ma- 
chines up to 100 horse power? 

16. Why are the brushes in a six-pole dynamo placed 
60 degrees apart? 

17. Explain why a six-pole armature with a wave wind- 
ing may have its brushes placed in the same position as a 
bi-polar machine? 

18. A four-pole wave wound armature has a flux of 
one and a half millions of lines; the speed is 1,200 revolu- 
tions per minute; there are 45 slots in the armature and 
each coil has four turns in it. What will be the voltage 
produced? 

19. What vrill be the voltage produced by the same 
armature if lap winding is used? 

20. What will be the relative resistance of the arma- 
tures with wave and lap winding? 

21. How may a lap wound armature for a four-pole 
machine be connected so as. to operate with two brushes? 



174 



22. What will be the difference in operation of a wave 
and a lap wound armature when the armature is not central 
in the pole pieces? 

23. \^^ly is it impossible to use an armature in a four- 
pole wave wound machine with an even number of slots if 
there are the same number of commutator bars as arma- 
ture slots? 

24. Make a diagram for a wave winding for a four-pole 
armature having 12 slots in the armature and 23 bars in the 
commutator? 

25. AVhat is a compound wound d;yT3amo? 

26. What is the object of putting a series coil on a 
dynamo? 

27. Why does the voltage of a plain sihunt wound 
dynamo decrease with the load? 

28. If a hi-polar dynamo produces 200 amperes and 
the shunt ampere turns are 2,600 on each coil and there are 
eight turns in the series coil, what will be the total ampere 
turns on each field coil at full load? 

29. What is the effect of compound winding on motors? 

30. What are the advantages of compound wOund mo- 
tors over plain shunt wound motors? 

31. Why will a 500- volt compound wound dynamo that 
operates very well on 500 volts greatly over-compound when 
operated at 250 volts? 



CHAPTEH XV. 



PROPEK METHODS OF CONNECTING UP DYNAMOS 

AND MOTORS. 



It is a fact, and one which for a long lime remained 
undiscovered, that a dynamo will excite itself when run at 
the proper speed and with proper connections between ar- 
mature and fields. It is also true that in order that a ma- 
chine may excite itself or excite its own field magnets, it is 
first necessary to send a current from an external source 
around the field magnets. This current drives a certain* 
amount of flux through the magnetic circuit, and since most 
of the magnetic circuit is composed of iron, a part of this 
flux does not disappear when the current is cut off. This 
permanent magnetism is called residual magnetism. The 
residual magnetism will be greater in a dynamo with an 
ironclad armature than in one with a smooth core, because 
the magnetic circuit is so much more perfect. The residual 
magnetism in most cases w^ill be greater with cast iron field 
cores than with wrought iron or soft steel. The amount 
of this residual magnetism with an ironclad armature varies 
from one to five per cent, of the total fiux with fully excited 
fields. The writer has seen a 500-volt street railway gen- 
erator w^hich had a residual magnetism such that it pro- 
duced 25 volts Wihen the armature was run at full speed. 
This residual magnetism produces a voltage in a certain 
direction depending upon the way in which the current has 



176 



been flowing* through the field coils and upon the way in 
which the armature is connected up to the commutator. In 
order that a dj'namo may excite itself, it is necessary that 
the current produced by the residual magnetism Sihall flow 
in such a direction as to sitrengthen this re- 
sidual magnetism. If the current produced by the 
residual magnetism flows through the field coils in the oppo- 
site direction this will tend to w^eaken the residual mag- 
netism and consequently to reduce the current which flows. 
If, on the other hand, the current produced by the residual 
magnetism flows through the field coils in such a direction 
as to strengthen it, the greater magnetism which results 
w-ill strengthen the current, and this in turn strengthens 
the field, and this process goes on until further increase in 
the magnetism is prevented by the saturation of some part 
.of the magnetic oircuit. It often -happens that 
w^hen an armature is re-wound tihe connecitions 
between the winding and the commutator are made in such a 
way as to reverse the direction in which current flows from 
the armature; that is, the brush which before the armature 
was re-w^ound was a positive brush may become a negative 
brush. This reversal of the direction in w^hich current 
flows in connecting up an armature is easily made and very 
frequently occurs. The re-wound armature when put into 
the old field produces a current which tends to flow^ in the 
opposite direction from that of the old armature. 

This current tends to reduce instead of strengthen the 
residual magnetism, and the result is that the machine will 
not excite itself or refuses to build up. In order to correct 
this difficulty, it is onlj'' necessary to reverse the connections 
between the armature and the field coil, so that the current 
produced by the residual magnetism may flow in suoh a 



177 

direction as to streng-then this residual magnetism. To do 
this either the leads from the armature may be crossed or 
the leads from the field may be reversed. When the fields 
have both series and shunt coils it is usually more conven- 
ient to reverse the armature leads than it is to reverse the 
leads from both series and &hunt coils. When, however, 
the field has only a single winding it will usually be found 
to be more convenient to reverse the field leads. An excel- 
lent method of determining whether the armature and fields 
are connected in such a way that the machine will not build 
up is to measure the residual magnetism with a volt meter 
with the field circuit open, then close the field circuit, and 
if the voltage drops it is almost a certain indication that 
the armature and field connections are reversed. In con- 
necting up a compound wound dynamo to its circuit it is 
necessary to be sure that the shunt coils and series coils 
tend to drive the lines around the magnetic circuit in the 
same direction. If the series coil is connected up in the 
opposite direction to -the shunt coil the dynamo will build 
up all right and will work satisfactorily on very light loads. 
When, however, the load becomes even, five or ten per cent, 
of full load, the voltage drops off very rapidly and it is im- 
possible to get full voltage with even half the load on. This 
is because the ampere turns due to the series coil decrease 
the total ampere turns acting on the magnetic circuit in- 
stead of increasing them as the load comes on. This lowers 
the magnetic flux and of course lowers the resulting volt- 
age. 

All shunt and compound wound dynamos are provided 
with a rheostat, which is placed in series with the shunt field 
magnetizing circuit. This rheostat is a resistance capable 
of adjustment by hand by means of which the current flow- 



178 



ing" throug^h the shunt first coils may be regulated. WTien 
this resistance is all cut out tne maximum current flows 
through tJie shunt fields and they consequenitly have a max- 
imum magnetizing- power and .the maximum voltage is pro- 
duced. If this voltage is too high, it is necessary only to 
insert more resistance in the shunt fields by a movement of 
tJie rheostat and thus cut dowm the magnetizing power of 
the fields and theo-efore the voltage produced by the dy- 
namo. 

It sonnetimes (happen-s that a dynamo refuses to build 
up because there is -so much resistance in the rheostat that 
'the current produced by the residual magnetism is not 
powerful enough to sutficienitly increase the magnetism of 
the fields to begin <the building up process. Therefore if a 
machine refuses persistently to build up it i's a good plan 
to short circuit the rheostat. This cuts out the resistance 
and at the same time bridges any possible open circuit that 
there may be in the rheostat. The rheostat should be ar- 
ranged so that the field circuit can never oe suddenly brok- 
en. This is to avoid the possibility of breaking down the 
insulation of the field coils by the so-called field discharge. 
A field discharge is said to occur when the shunt circuit of 
a dynamo in operation is suddenly opened. Anyone w^ho has 
done this knows that a very lomg thin arc is produced; the 
length of the arc ind/rcates the high voltage produced by 
the discharge and the small size of the arc shows that the 
current is compa.ratively weak. A calculation will show 
what the voltage produced by such a field discharge may be. 
Suppose a shunt field of a 110-volt dynamo is composed of 
two coils each of 1,500 turns, also that the magnetic flux 
pas9(ing thrugh these coils amounts to 4,500,000 lines. If 
this circuit is opened in one second, the voltage which would 
be produced will be 2x1,500x4,500,000 divided by 100,000,000 



179 



o*r 135 vdl.ts. When the field circuit is opened in 1-100 of a 
second, tihe voltage will be 

1,500x2x4,500,000 



100,000,000 1,500x2x4,500,000x100 

equals 

1 100,000,000 

100 

or 13,500 volts. Such a voltage as this is very apt to punc- 
ture the insulation of a field coil and care should be taken 
that the circuit is never opened in such a way as to expose 
the Insulation to such a strain. The production of an ex- 
tremely high voltage in this manner is simply a reproduc- 
tion on a larger scale of the ordinary battery and spark 
coil used for igniting gas engines. In the ordinary spark 
coil the current from a battery of two or three volts is 
passed around a magnet and then suddenly opened with 
the production of a spark from one-fourth to one inch in 
length. Here we have the production of many hundreds of 
volts from two or three. The same multiplication takes 
place when a shunt field is opened suddenly. 

Rheostats for the shunt circuit of a dynamo should have 
sufficient resistance, so that when it is all inserted the volt- 
age in the dynamo will slowly sink to zero. This method 
of stopping the action of a dynamo is perfectly safe and 
should be followed wherever possible. Fig. 66 shows an- 
other diagram of the connections of a compound wound 
dynamo. 

Almost all stationary motors are plain shunt wound 
machines. Fig. 67 is a diagram of the way in which these 



ISD 



motors should be connected up. The essential point in 
this scheme is that the shunt field circuit be always closed 
through the rheostat and armature so that a field discharge 
is impossible. The rheostat is inserted for the purpose of 
not permitting too great a rush of current through the 
armature before it has attained its speed and consequently 
its counter E. M. F. 




Figure 66 
Diagram of connections of compound wound dynamo. 



If this rheostat were arranged so that when it was 
thrown off, the armaiture circuit should be opened, the open- 
ing of the main switch would break the current through tihe 
shunt fields and produce a field discharge. An arrangement of 
a starting rheostat like this has been >the cause of numberless 
burn-outs in field coils. If, however, the resistance of the 
starting rheostat is simply sufficient to choke the current 



181 



back to the desired amount and does never open tlie arma- 
ture circuit, the opening of the main switch simply cuts 
the current off the motor. The instant after the main 
switch is opened the motor armature becomes a dynamo 
armature at practically the same voltage and supplies the 
field coils with current almost as long as the armature 
continues to revolve. In this way there is absolutely no 
possibility of such a disturbance of the shunt circuit such as 
will produce any abnormal strain on the insulaJtion. 




Figure 67 
Diagram of connections of plain shunt wound motOFo 



An automatic rheostat or starting box is one which is 
provided with a spring, which tends to throw the handle 
back to the position of greatest resistance. (See Fig. 68.) 
A magnet holds the handle in opposition to the spring in 
that position in which all the resistance is cut out. The 



TS2 



mag-net is usually energized by the current which passes 
throug'h the shunt coils on the motor. If, for any reason, 
the power which operates the motor should fail, the mag- 
net will w^eaken and rele^ase its hold. The spring w ill force 
the handle back to the position of greatest resistance, and 
when the power is ag'ain thrown on the line the motor will 
start up in the ordinary way. 




Figure 68 
Diagram of automatic starting box showing connoetioas. 



If the resistance in the starting rheostat were entirely 
cut out and the power was thrown onto the motor from 
ten to a hundred times full load current w^ould flow through 
the armature, causing* very bad sparking- and almost cer- 
tainly blowing the fuses which protect the motor. 

Overload rheostats are those in which the resistance is 
cut in where the current exceeds a certain amiount. 



183 

In one desig-n of overload rheostat the magnet spok- 
en of above has two windings, a shunt winding which is 
the more pow^erful and a series winding in oppositon to it. 
With normal load the series winding does not diminish the 
strength of the magnet sufficiently to release the rheostat 
handle, but with an overload the magnet is weakened suffi- 
ciently so as to release the rheostat handle and insert the 
resistance of the starting rheostat in the armature circuit. 



QUESTIONS ON CHAPTER XV. 



1. What is the effect of residual magnetism in the self- 
excitation of dynamos? 

2. 'Would a dynamo in which there was no residual 
magnetism excite itself? 

3. Why will reversing the connections of the shunt coil 
prevent a dynamo from generating? 

4. What is the amount of residual magnetism in or 
iinary iron-clad dynamos? 

5. When a machine begins to build up, \v*hat causes 
the voltage to stop ris.ing? 

6. Tf a dynamo could be made vdthout iron that would 
build up if supplied with a residual field from an external 
source, what would be true of the voltage generated by 
such a dynamo? 

7. If an armature fails to build up, what course should 
be pursued? 

8. How is it possible to be certain that the armature 
and field magnet connections are properly made w^ith refer- 
ence to the residual magnetism? 

9. How will a compound wound dynamo act when the 
series and shunt coils are reversed? 

10. W^y does moving the arm of a rheostat r5ise or 
lower the voltage cf a shunt or compound wound dynamo? 

11. What is a field discharge? 



185 

12.. What will be the voltage from a field discharge 
from the Edison dynamo on Fig. 26, if /there are 1,500 turns 
on eacii coil and the circuit is broken in 1-50 of a second? 

13. What will be the voltage produced if there am 
5,000 turns on each coil and the circuit is broken in 1-80 of 
a second? 

14. How should the rheostat in series with the shunt 
ooils of a dynamo be arranged? 

15. Why is it desirable to have a starting box for a 
shunt wound motor that will never break the circuit? 

16. Explain why a field discharge is impossible witii a 
starting box arranged in this way. 

17. What is the object of the automatic starting box? 

18. How are overload automatic rheostats arranged? 



CHAPTEK XVI. 



DISEASES OF DYNAMOS AND MOTORS: THEIR SYMP- 
TOMS AND HOW TO CURE THEM. 



A. — Open Circuits. 

The currenit in an armature flows from sectiooi to sec- 
tion of the armature winding* and usually has to pass to 
the commutator to pass from one section to the next. Oc- 
casionally one of the lead w^ires from the armature wind- 
ing to tlhe oom/muttaitor becom'es broken; this prevents the 
armature current form flowing* through this path in the 
armature. But it will be noticed that when the coil con- 
taiTiing the broken wire is s.hort circuited by the brush, 
current will flo»vv througih 'the w^hole armature in a normal 
manner. As s-oon, however, as this coil leaves the brush 
the armature current in attempting to complete its circuit 
through this half of the armature wdading w^ill arc from 
one commutator bar to the next one in its attempt to flow 
through the circuit in spit'e of 'the broken w^ire. This arc 
will show itself as a very bad spark at light loads or as a 
ring of Are traveling around the commutator if the voltage 
is high enough to keep up the arc. With heavy loads ■t'h-e 
sparking becomes very furious and the insulation which 
separates the two com^mutator bars betw^een which the arc 
occurs will be melted out. Any one who has omce seen the 
effect of an open circuit on a commutator cannot fail to 
recognize it if s^en a second time. It ma}^ be that the 
o]>en circuit is caused b^^ the melting of the solder, which 



187 

attaches the armatiure wire to the commutartor bar. If the 
armature winding* is coimpleted by having the outside of 
one coil and the inside of the next coil soldered into the 
coonmutator bar the melting- of the siolder will make a true 
open circuit. If, however, the connection between the ar- 
majture winding- and the commutator bar is such as is 
shown in Fig-s. 57, 58 and 59, the open circuit will be only 
partial and will show itself only in increased sparking*. 

The cure for am open circuit is obviously to find the 
broken wire and repair it. If the trouble has been due to 
the melting' of the solder in the commutator bars these 
wires should be thoro'ughly re-soldered at once. If, how- 
ever, the wire is broken in the armature somewhere and it 
is desired to operate the machine temporarily, the two bars 
across which the arc occurs may be soldered tog-ether or 
connected together in some other way, so that the arma- 
ture current may be able to complete its circuit through 
this temporary bridge. It is possible to run an armature 
temporarily repaired in this way for several weeks with- 
out serious trouble. 

B. — Short Circfuits. 

« 
If, in a properly wound and connected armature, two 

of the commutator bars be connected together, the voltage 

which is produced in the coil connecting these bars will 

produce <a very great local current, which will flow through 

the coil and complete its circuit acress the two commutator 

bars. Such a connection would be a short circuit, and any 

connection that allows a local current to flow through a 

part of the armature winding is called a short circuit. 

Suppose an armature with a resistance of 1-10 of an 
ohm has fifty coils; the resistance of each path in the ar- 



188 

mature will be 1-5 of an ohm and the resistance of each 
coil will be 1-25 of 1-5, or 1-125 of an ohm. If, now, this 
armature is capable of producing 250 volts each coiil in it 
generates 10 volts on the average. When the armature is 
working property this 10 volts simply adds itself to the 
voltage produced by the other coils la.nd is expended in 
forcing the arm>ature current through the external resist- 
ance. If, however, the two bars to which this coil is con- 
nected be short circuited, this 10 volts will expend itself in 
producing a \ery great local current through this short 
circuited ooil. The coil generates 10 volts and its resist- 
ance is 1-125 of an ohm. The current which wull flow then 
will be 1,250 amperes; this is enough to heat the coil red 
hot and entirely destroy the insulation in its neighbor- 
hood. Trouble of this sort is the most des'tructive that can 
occur in an armature, for it usually compels the re-winding 
of the whole armature. If the short circuit is discovered 
before the coil has been sufficiently heated to destroy the 
insfulation, and it ds absolutely necessary to use the arma- 
ture temporarily and the point at which the coil is short 
circuited cannot be discovered, eaclh turn of the short cir- 
cuited coil may be cut in two and then the two commuta- 
tor bars beitween which tiiis coil is connected may be s-old- 
ered together. It often happens that one wire in a coil 
touches its neighbor at some point, and when this occurs 
only one turn of the coil will be short circuited and only 
one turn will get hot. 

A sJiont circuited coil always siliows itself by getting 
wanner than its neighbors at first, and if not soon discov- 
ered will smoke and finally set fire to the insulation. 

If an armature is completely short circuited, as, for 
instance, from top to bottom layers in a horizontally wound 
armature or fro-m coil to coil in a vertically wooind arma- 



189 

tuTe, it will refuse to build up if it is a genevastor and will 
turn a half revolutiooi at a time if it is a two-pole motor, 
or a quarter revolution if it is a four-pole motor. In a bi- 
polar machine the short circuit of the armature will not 
affect the distribution of the current when the short cir- 
cuit is 90 degrees froon the brushes, for then the two oppo- 
site^, sides of the commutator are at no difference of poten- 
tial and no current will flow in the short circuit. 

C. — Sparking. 

The principles which govern perfect commutation were 
explained in the chapter on "Sparking," but many other 
causes beside improper design of the dynamo may cause a 
machine to spark. When the commutaitor is in good con- 
dition, trueand smooth, and the brushes have a firm con- 
tact against it and the machine invariably sparks at a 
heavy load, the trouble may be attributed to a poor design. 
In a well de-signed machine the causes for sparking will be 
a rough commutaitor, a commutator out of round, or 
brushes not having sufficient contact against the commu- 
tator. 

In fact, the causes of sparking may be divided into two 
classes— sparking from electrical causes and sparkin^^ from 
mechanical causes. The cause of the electrical sx^arking 
was explained in Chapter XV. 

In most machines built at the present time any spark- 
ing that there may be is principally due to mechanical 
causes. It is clear that in order to have sparkless running 
the brushes must at all times touch the commutator. The 
fact that from some cause or other the brushes do not touch 
the commutator all the time is the cause of most cases of 
sparking. If the brush is not free to move, sparking will 



190 

result, for even in the best machines there will be some 
movement of the commutator with reference to the brush, 
and if the brush cannot follow it there will be a very short 
arc that maybe will n-ot be seen until the oommutator is 
blackened and burned at one spot. 

When an armature is slightly out of balance and is run- 
ing at a very high speed, there will be a vibration of the 
commutator, and if the machine is to run sparkless the 
brushes wull have to follow this vibration of the commu- 
tator. In order that the brush'es may follow the movements 
of a commutator that is not running perfectly true, the mov- 
ing part of the brushholder should be as light as possible and 
the spring tension that holds the brush against the commu- 
tator should be as heavy as possible. This condition is best 
fulfilled in a brushholder in which the brush alone moves, 
for in such a brushholder the inertia of the moving part is 
as small as it is possible to obtain, and consequently a com- 
paratively small pressure will enable such a brush to follow 
the uneven motions of the surface of the commutator. 

The writer once saw a motor which ran at 3,700 revolu- 
tions per minute, which could not be prevented from spark- 
ing when solid brushes were used, owing to the fact that 
the commutator did not run perfectly true. When leaf cop- 
per brushes were employed on this same commutator the 
motor ran almost sparkless, due to the fact that the copper, 
with its large number of separate leaves, always made con- 
tact with the commutator. Another cause which prevents 
the brush from touching the metallic part of the commuta- 
tor is the use of insulation between the commutator bars 
that does not wear down as fast as the commutator bars 
themselves. After the machine has run for a time these 



191 

insulations project above the copper bars and produce both 
heating and sparking. Poor construction of the commu- 
tator is another prolific cause of sparking. If the commu- 
tator is not perfectly tight the centrifugal force will throw 
out one bar more than its neighbor, and consequently there 
will be spots on the commutator that the brush cannot 
make contact with. A commutator must be mecTianically 
clean in order to run sparklessly. Spots of paint or dirt 
may be on a coimmutator and get between the brush and 
the copper bar, and so prevent perfect contact at one point 
in the commutator and produce sparking. 

A cause which produces as much sparking as improper 
mechanical arrangement of the brushholder is improper set- 
ting of the brushes. As explained in the chapter on spark- 
ing, there is a proper place for the brushes, and if they are 
not placed in this position there will be a tendency to spark. 
The brushes being in a wrong position will first heat the 
commutator and roughen it, and when the surface of the 
commutator is impaired, sparking will result. In a dynamo 
the brushes should be rocked forward in the direction of 
rotation into such a position at no load that the voltage is 
two or three per cent, lower than the maximum voltage. 
In a motor the brushes should be rocked backward into such 
a position thai ^t no load the speed is increased about two 
per cent, above t<he lowest speed. 

D. — H>i^ating the Commutaitor. 

Abnormal heating of the commjtaftor is due VO One of 
four causes: First, friction of the brush against the Com- 
mutator; second, improper position of the brushes SO that 
there is forced commutatiooi; third, abnormally heavy cur- 
rents being taken from the armature; fourth, poor contact 



192 

between brushes and commutator. As soon as it is deter- 
mined to which of these four causes the heating is due, the 
remedy in each case is obvious. The heating of the com- 
mutator in many instances may be rem-edied by the substi- 
tution of copper brushes for carbon brushes. First, because 
the friction between the commutator and the copper brush 
need not 'be so great a-s between the commutator and the 
carbon brush, and still more important because the electri- 
cal resistance between the commutator and the brusih is 
very much less with the copper than with the carbon. The 
objection to the use of the co|)per brush on any commuta- 
tor is that unless it i's given very careful attention it will 
cut the comimutator in the same way and for the same 
reason that a bearing without oil will cut. 
E. — Grounds. 

When a machine is out of order the first thing to do in 
testing it is to find whether or no there is a connection be- 
tween the winding and the frame of the dynamo or motor. 
Such a connection is called a ground. A single ground on 
a machine does not of itself impair its action; it only ren- 
ders the insulation in some other part of the machine very 
liable to break down. When there are two grounds on a 
machine there will be a short circuit of more or less of the 
winding, for the current will run from one part of the 
winding through one ground through the frame of the 
machine through the second ground to the other part of 
the winding. Such a short circuit usually shows itself 
very plainly by burning the insulation and usually stop- 
ping the operation of the machine. 

Some motors, as, for instance, street car motors, are 
built with one end of the winding grounded to the frame. 
The object of this is to allow the current after it has pasa- 



193 

ed througli the motor and done its work to escape tlhrougli 
the motor frame, axles and wheels of the car to the rails. 
When such a motor as this is to be tested for a ground it 
is necessary to open the connection between the winding 
and field frame before the test is made. Testing for ground 
is usually done with a small dynamo provided with a field 
made of permanent magnets and operated by hand. When 
current passes through thie circuit its pres'ence is made 
known by the ringing of a pair of small bells. 

Partial grounds, as, for instance, in the mica insulation 
of a commutator, may cause severe heating of a part of the 
commutator, due to the arc that is formed between the 
coonmutator bars and the commutator core. It is possible 
by the use of a Wegton volt meter to determine just w^here 
the ground is in an armature, provided the ground is per- 
fect or nearly so. Pass current from an external source 
between the armature core and the Avinding, and test the 
voltage when the wire carrying the current rests upon a 
certain commutator bar. Next, move the wire carrying the 
current four or ^ve bars in one direction, and measure 
the voltage again. If the voltage is higher in the second 
case than in the first, it is clear that the current passes 
through more of the armature ^vinding in the second case 
than in the first. It will be necessary then to move the 
other way. Keep on testing in this manner until a bar is 
found that gives the lowest voltage. Either the ground is 
in this commutator bar or it is in the armature winding in 
tihe coil that is connected to this bar. To determine this 
point, unsolder the 'armature wire from the commutator 
bar and test each separately. Even when the ground is 
imperfect it is possible to locate it within one or two bars 
of its exaot posdton. The armature wires may be unsold- 



194 

ered from several commutator bars and each coil tested 
separately with a mag*neto bell. 

A single ground between a series and a shunt coil may 
practically short circuit a dynamo, for the series and 
shunt coils are connected tog*ether on one side of the ma- 
chine, and if a ground should occur between the other ex- 
tremity of the shunt coil and a series coil, a complete short 
circuit vrould result. 
r. — Open Circuit in Field Coil. 

If for some reaison one of the wires in the shunt field 
coil of a mo'toror dynamo should become broken, the ma- 
chine w^ould nort operate, because it would be impossible to 
produce any magnetic flux. This would show itself in a 
d^'namo by the refusal of the mp/^hine to build up. In a 
motor it would sho/w itself by the ^ '='fusal of the motor to 
pull any load and by blowing the iases when the starting 
rheostat is nearlj^ cut out. In a motor a very easy way 
to test this is to- see whether the fields are excited as soon 
as the switch is closed by presenting a knife or any mag- 
netic object to the magnet pole. Another way of maldng 
the lest is to open the armature circuit and close the 
main switeh, and then open it slowly. If the field wire is 
broken there will be no current; if the field is in perfect 
conditon there will be an arc upon the opening of the 
switch. If there are two or more field coils on the motor 
it is easy to determine the one in which the broken wire is 
situated b}^ turning on the current and then short circuit- 
ing one after the other until one is found which, when 
short circuited, allows the current to flow through the 
other coils. This coil will have to be removed and rewound. 

G.— Short Circuit in Field Coils. 

If, for any reason, the beginning and 'end of a coil come 
in contact, the resistance of the coil between these two 



ts. 



195 

points is cut out, and the current will flow only through a 
part of the coil. In practice this coil will show itself by run- 
ning cooler than the others, because the same current runs 
through a greater resistance through the other coils than in 
the short circuited ooil. By measuring the voltage across 
the damaged coil and across a good coil thir amount of the 
damaged coil which is short circuited may be determined. 
This coil will have to be removed and rewound. If, from 
any cause, such as long use or improper ventilation, the 
insulation on the wire in a coil becomes charred, so that it 
IS no longer a good insulator, the current, instead of flowing 
through all the turns of a coil, will leak from layer to layer 
Such a coil is said to 'be "burned out," and mav be detected 
by running cooler than a coil in good condition and by 
having very much lesf,. magnetizing power. It is to be 
observed that when a shunt field coil becomes short cir- 
cuited or "burned out," it throws a great deal more load 
on the other field coils; for instance, if there are two field 
coils on a motor which normally take one ampere at 220 
volts, the watts wasted in each coil will be 110. If now 
one of these coils be short circuited, the only resistance in 
the circuit will be that of the other coil, and the current 
through this coil will be two amperes, because one .oil has 
on.y half the resistance of two. The voltage on t^^is coil 
will be 220 volts; therefore 440 watts will be wasted in it, or 
four times the normal heat loss. It is easy to see that if 
one coil should become short circuited this would be almost 
certain to burn out the other coil. 

H.— Improper Connection of Field Coils. 

It is easy to see that in order to be effective the field 
coil must be connected up in such a way that it forces the 
flux around the circuit in the same direction 



196 

that its mat^s do. Thus in the Edison dynamo 
shown in Fig. 23, if the field coil should be 
connected up in such a direction as to make both pole 
pieces north poles, it is obvious that there would be no 
magnetic flux through the armature. If this machine were 
used as a motor the armature would not run with even a 
small load. In order to detect this trouble it is necessary 
to test the polarity of the field coils with a compass. If it 
is found that both poles are the same it will be necessary 
to reverse the connections of one of the field coils. If the 
field coils should be connected up in this way on a dynamo 
it would refuse to build up, and the only way to detect the 
trouble would be to send current through the field coils 
from an external source and test the polarity of the pole 
pieces with a compass. Great care should be taken when 
putting on a repaired field coil to see that it is connected up 
correctly. 

I.— Heating of Field Coils. 

When all the field coils on a new machine rise to a tem- 
perature of over 70 degrees Fahrenheit above the surround- 
ing air they are too warm to be chirable, and it is an indi- 
cation that not enoug^h wire has been used in the field coil 
by the manufa<iturer. 

When on an old machine a coil gets warm while an- 
other is much cooler, it is, as explained above, usually due 
to a abort circuit or a partial burn out in the cool coil. 
The coil that is hot is the one that is still in good condi- 
tion. The only way to prevent the heating in all the shunt 
field coils is to increase the amount of wire on the coils. 
J. — Noise When a Machine is in Operation. 

In machines having ironclad armature a humiming or 
singing noise is ocoasionally heard when the armatures run 



197 

with fully excited fields. This occurs in machines which 
have short air g'aps usually, and is due to the anagneftic pull 
exerted on the tooth of the armature as it suddenly comes 
under the influence of the field magnet. The mechanical 
force due to the magnetic attractino between the armature 
and field magnet is sufficient to mechanically stretch out 
the tooth a fraction of a thousandth part of an inch. This 
produces a small air wave and a rapid successiooi of these 
as the armature passes under the field magnet produces 
the noise. 

In itself the noise is not harmful but is occasionally 
an indication of tufting o'f the magnetic lines as they pass 
from the pole piece into the armature teeth. As was 
learned in a former chapter, this tufting of the magnetic 
lines produces eddy currents in a solid pole piece which 
wastefully heats it. 



^ 



1 



QUESTIONS ON CHAPTER XYl. 

1. What is an open circuit? 

2. How does an open circuit show itself? 

3. How may an open circuit be temporarily repaired? 

4. What is a short circuit? 

5. How much current will flow in a short circuited 
coil in a 110-volt armature, if there are 40 sections in the 
commutator and the resistance of the armature is 2-100 of 
an ohm? 

6. How will a short circuit show itself? 

7. What will be the eft'ect of a short circuit between 
the upper and lower halves of a horizontally wound arma- 
ture? 

8. How will a short circuited armature operate in a 
motor? 

9. W^at is the most ordinary cause of sparking? 

10. What is the principal mechanical necessity in or- 
der to prevent sparking? 

11. Name some of the causes which prevent the brushes 
from touching the commutator continually? 

12. What is the objection to a heavy brush holder with 
a carbon brush rigidly clamped into it? 

13. "What is the effect of improper setting cf the 
brushes? 



199 



14. In what direction should dynamo brushes be rock- 
ed as the load increases to prevent sparking? 

15. In what direction should motor brusihes be rocked*? 

16. What are tour causes of heating the commutator 
of a machine? 

17. What I's a ground? 

18. Whait is the effect 'of two grounds on the same 
machine? 

19. Is it possible to successfully operate a grounded 
machine? 

20. What is necessary to do before a street car motor 
can be tested for a ground? 

21. How is it possible with a Weston volt meter to 
locate the position of a ground on an armature? 

22. How may a ground between a series and a shunt 
coil short circuit a machine? 

ii3. How will an open circuited field coil show itself? 

24. How is it possible to locate an open circuited field 
in a motor? 

25. What is the effect of a short circuit in a field co:l? 

26. Why will a short circuited field coil run cool while 
a short circuited armature coil becomes very wai'm? 

27. Why will one short circuited field coil almost cer- 
tainly burn out its mate if there are only two on the ma- 
chine? 



([^ 



200 



28. W%at is the effect of improper connection of the 
field coils? 

29. AYhen all the field coils on a dynamo or motor run 
warm ihow can they be made to run cooler? 

30. What is the cause of the humming noise sometimes 
heard in machines ivith iron-clad armatures? 



CHAPTER XVII. 



ARC AND INCANDESCBXT LAMPS. 



A large part of the electric power which is produced at 
the present time is used for electric lighting. To produce 
this light two devices are used; one is called the incandes- 
cent lamp, the other the arc lamp. In the incandescent lamp 
a comparatively small amount of current is forced through 
a thin carbon wire of very high resistance. This carbon 
wire is enclosed in a glass bulb which is completely ex- 
hausted of air and is supposed to contain nearly a perfect 
vacuum. 

The object of extracting the air is two-fold: First, if 
any oxygen (were left inside the bulb, the caribou when at a 
high temperature would greedily combine with all the oxy- 
gen in the globe, or the filament would burn up. Another 
reason w^hy a vacuum is desirable is that if there were 
gases inside the bulb the heat of the filament would be more 
readily dissipated, because the particles of gas would be 
heated very much by contact with the incandescent carbon 
filament and then pass to the glasis walls of the bulb, and 
give up their heat to it, and then return to the filament 
to be re-heated. In other words, if there were gases in the 
bulb, the incandescent filament would lose its heat through 
both radiation and conduction. When all the gases are 
exhausted from the bulb the only loss is the loss by radia- 
tion. 



202 



The current is broug'ho to the carbon fil- 
ament by two platinum wires which are melted 
into the glass. It is necessary to use platinum wire 
for this purpose, for the reason that platinum and glass ex- 
pand with rise of temperature at about equal rates; all oth- 
er metals expand about twice as rapidly as glass does, and 
contract twice as fast, so that if iron wires were fused into 
the glass at a high temperature, a small space would be 
left between the wire and the glass w^hen the wire was cold, 
through which the air comld slowly creep and spoil the 
vacuum. 

The light given off by an incandescent lamp increases 
very rapidh" with the temperature. A lamp on 100 volts is 
nearly as hot as when at 110 volts, but only gives about 
half the light. 

Tt is desirable to work the lamps at as high a tempera- 
ture as possible, in order to get as much light as possible 
out of them, but the higher the temperature or voltage at 
which they are worked the sooner they burn out. 

A lamp may give a very good light at 110 volts and last 
for 600 hours that would not last 100 hours on 112 or 113 
volts. A Yevy necessarj^ condition to the long life of an 
incandescent lamp worked at a very high temperature is 
that the voltage be constant. 

Therefore, for the successful operation of high efficiency 
lamps, or those in which the carbon filament is very hot, a 
very steady and unvarying voltage is essential. The most 
common incandescent lamp produces about 16 candle power, 
is operated at 110 volts and requires from 2^4 to 4 watts per 
candle or from 40 to 64 watts for the lamp. As an average, 
it may be said that each lamp takes Vo ampere at 110 volts. 



203 

or 55 watts; that is, about 3l^ watts per candle. As the in- 
candescent lamp gets old the light that it produces gets 
weaker until it becomes so poor a device for transforming 
electric energy into light that it pays to take the lamp down 
and substitute a new one. 

It is likely that some time the heat in the filament of 
an incandescent lamp will be used as the heat from the gas 
is in a Welsbach gas burner, to heat an oxide that has the 
faculty of giving off a great deal more light at a low tem- 
perature than carbon has. If this could be successfully 
done it woiild very greatly increase the light produced by 
the Incandescent lamp. 

The arc lamp is best adapted for lighting streets or 
large areas in an interior. In the arc lamp a small part of 
a pencil of carbon is heated intensely by the passage 
of a considerable current from one pencil to another across 
an air space. The carbon is heated to about 7000 degrees 
F. until it probably vaporizes, and this very hig^h tempera- 
ture produces the most intense light that is known. 

The ordinary incandescent lamp requires 3l^ watts per 
candle power. 

A current of 10 amperes at 45 watts produces 2000 can- 
dle power in an arc lamp, or about 4^4 candle power per 
watt. 

The objection to the arc light is that it is so intense that 
it casts deep shadows and dazzles the eye. This ditficulty 
has been partly overcome in the enclosed arc lamps that are 
coming into such general use. 

» In these lamps the arc is produced in a glass globe that 
is arranged so that very little fresh air can get in. 



204 



The oxygen in the globe is very soon consumed by the 
carbon and the carbon thus burns away much more slowly 
than it would in the open air. 

The arc lamp must be provided with automatic mechan- 
ism that will feed the carbon dow^n as fast as it is consumed 
and so keep the arc the same length. The mechanism for 
accomplishing this result in the old lamps was in some 
cases quite complicated, but in the modern lamp there is 
very little mechanism. 

In general, the operating mechanism of an arc lamp is 
composed of a magnet that grows weaker as the arc gets 
larger, and at a certain point grows weak enough to release 
a clutch that allows the carbons to come closer together. 




Figure 69 
plagram showing action of series arc lamp, 



205 

Before tlie carbons can drop together the current through 
the lamp is changed and the magnet strengthened and the 
motion of the carbons arrested, and they are drawn a prop- 
er distance apart. 

Figs. 69 and 70 are diagrams tha^ illustrate the action 
of the series lamp and the modern constant potential lamp. 

In the series lamp, in which the strength of the current 
is constant, the strength of the magnet is varied by using 
a series coil and a shunt "Coil in opposiition to it. The ^hunt 
coil is connected across the arc and when the arc is long 
the current in this coil is greait and the strength of the com- 
bined series and shunt coils is small, thus allowing the car- 
bons to drop together. 




Figure 70 
Diagram showing action of constant potential arc lamp. 



QUESTIONS ON CHAPTER XVII, 



1. How is the light produced in an incandescent lamp? 

2. Why is a vacuum necessary in the bulb of an incan- 
descent lamp? 

3. W'hj^ is it necessary -to use so expensive a metal as 
platinum to carry the current to the carbon filament 
t'hroug-h the glass? 

4. W.hat is the necessary condition of the voltage of 
supply to produce a bright light and a long life in an in- 
candescent lamp? 

5. How many watts are used in an ordinary 16-candle 
power incandescent lamp? 

6. When does' it pay to destroy an incandescent lamp 
and substitute a new one? 

7. What is the temperature of the electric arc? 

8. How many watts per candle power are required in 
an arc? 

9. Why do the modern inclosed lamps give better illu- 
mination but less light than the old style open arcs? 

10. Why do the inclosed arc lights burn so much long- 
er than the open arcs? 

11. Describe the feeding mechanism in a constant cur- 
rent arc lamp. 



CHAPTER XVm. 



MEASURING INSTRUMENTS. 



There are a great many instruments used for measuring 
various electrical quantities, but all that can be considered 
in this chapter are volt meters and ammeters of the more 
common type. 

Common volt meters are really ammeters with a very 
high resistance in circuit and so arranged that the current 
w^hich passes through them is proportional .tlo the voltage; 
therefore what the meter actually measures is the amount 
of current that passes through it, but as the cur- 
rent is proportional to the voltage, the movemenits of the 
measuring instrument may be made to read volts direct. 

Fig. 71 is a diagram showing the way in which a Weston 
meter is constructed. This is an excellent illustration of 
the fundamental fact on which the operation of motors de- 
pends. 

A permanent magnet M causes magnetic flux to flow 
across the gap G; situa.ted in this gap is a bobbin B, on 
which are wound a number ^of tunnis of copper wire. The 
bobbin is made of copper and is arranged to revolve on 
jewel bearings. Two springs S,one above and one below the 
bobbin, carry the current from the movable bobbin to the 
stationary part of the meter. If current is now passed 
through the bobbin by way of the springs, the current will 



208 



flow downwards on one side of the bobbin and upward on 
the other side. Thus the current in both sides of the bobbin 
produces a torque which moves the bobbin against the force 
of the two hair springs S. The bobbin will continue to 
move until the torque exerted by the current equals the 
counter-torque exerted by the two springs. A pointer reg- 
isters the amount of motion and the position of the pointer 
is read off as volts. 




Figure 71 
Diagram of connections and moving parts of Weston voltmeter. 



A little examination will show that the torque exerted 
by the wires carrying the current on bobbin B is propor- 
tional to the current, for the flux is constant throughout 
the whole air gap. Tt is also true that the counter-force 
exerted by the two hair springs is proportional to the move- 



209 



ment of the bobbin; therefore twice as much current in 
the wires or the bobbin will produce twice as much move- 
ment of the pointer over the scale. The magnet M is made 
of Tungsten steel and is artificially aged, so that when the 
instrument is turned out of the factory the magnetizing 
power of the magnet will remain constant for years. 




Figure 72 
Connection of Weston ammeter. 



Current is brought into the instrument through the 
binding j>osts A and C, but, before passing through the wire 
on the bobbin, the current must traverse the very high re- 
sistance R; this resistance is from 65,000 to 75,000 ohms for 
a volt meter intended for a 600-volt circuit. Therefore the 



y- 



210 



current whicli passes through the wires on the bobbin, even 
with full voltage, is very small, and with 100 volts will be 
not much over 1-700 of an ampere. Yet this small current 
is able to produce very considerable deflection in the two 
hair springs w^hich resist the motion of the bobbin. An- 
other very excellent point in the design of this meter is the 




Figure 73 

MaCTJetic vane voltmeter depending on repulsion of two 
similarly magnetized iron strips. 

way in w^hich it is made deadbeat, or the way in which the 
needle is prevented from vibrating back and forth on each 
side of the point at which it will finally come to rest. The 
bobbin B is made of copper, and when it moves there will be 
crenerated in it currents which, according to Lentz's law,tend 



211 

to prevent its motion. The mechanical momentum given to 
the bobbin by the action of the current in the wires that 
are wound on it is absorbed by these Foucault or eddy cur- 
rents in the copper bobbin. The Weston direct current me- 
ters are almost perfectly deadbeat. 




Figure 74 

Western electric m^^ effort of iron strip to get into 

as powerful field as possible, or to get as near to the 

wire carrying current as possible. 

In Fig. 72 is a sketch of the Weston di- 
rect current ammeter. The working parts -are precisely 
the same, the principle of operation is identical, and it 
would b^ impossible to tell the two dnstrument.s apart, 
so far as the actual indicating mechanism is concerned, if 
It were not that the bobbin is wound with coarser wire. 



212 



The wire on the bobbin is a shunt on the resistance H. The 
whole current to be measured passes through the meter 
from binding- post A to post C. In doing so it has to pass 
throng-h the resistance R. The voltage at the extremities 
of this resistance Is, according to Ohm's law, proportional 




Figure 75 

Brush Electric Co. voltmeter and ammeter in which the attraction 

of a Solenoid for an iron core is weighed. 

to the current; or, looking at it in another way, the current 
will divide between the* resistance R and the bobbin B in- 
v*».rsely proportional to their resistances. Therefore, when 
a large current is passing through R, ^ oorrespondingly 
Jarge current is passing thrn^^gh bobbin B. As we have 



213 



seen m Fjg. 71, the position of the pointer registers th« 
amount of current passing through the bobbin, and it will 
be seen that the position of the pointer may be read off 
directly as amperes. 

A large class of the cheaper measuring instruments de 
pend for their action upon the attraction of a solenoid for 








Figure 76 



2U 



a piece of iron. The attraction of the solenoid is balanced 
by a spring or gravity and the position at which equilibrium 
occurs is a measure of the attracting force, and therefore a 
measure of the ampere turns in the solenoid. Whether the 
position of the pointer is to be read off as volts or amperes 
depends on whether the coil is wound with fine wire or 
coarse wire. 

A serious objection to these instruments in so far as 
their accuracy is concerned, is that they will record higher 
values on descending amperes or volts* than on ascending. 
This is due to the residual magnetism. When a current of 
25 amperes would pass through the meter this would cause 
a certain number of lines of force to pass through the iron 
part of the meter. When the current sank to 23 amperes 
a certain number of lines due to the 25 ampere current 
would still remain in the iron, aind this number would be 
greater when the current would pass from 25 amperes to 
23 amperes than when it passed from 21 to 23 amperes. 
The mechanical force acting on the iron would be greater 
in the first than in the second case and therefore the am- 
peres indicated will be higher. Error due to this cause 
amounts to from 2 to 10 per cent., depending on the con- 
struction of the meter. Fig. 73 shows one stj'le of mag- 
netic vane meter. Fig. 74 shows the meter built bv the 
Western Electric to. Fig. 75 shows a style of meter for- 
merly built by the Brush Electric Co. Fig. 76 shows the 
type of meter bnilt by the Westinghouse Electric Co. 



215 



THOAIPSOX KBCORDING WATT METER. 



Most of tihe recording mefters in use in this country are 
of this type. In general, the meter is simply an ordinary 
motor, except that it is built without iron, ais shown in 
Fig. 77. Attached to the shaft of "this motor is a retarding 
dis«c, which is made of copper and is revolved between per- 
-manent field magnets. The field coil in this meter is usu- 
ally made of coarse wire, and through it pa/s-ses the current 
to be meas-uired. The armature i-s wound up with fine wire 




^^JIMJE 



Figure 77 

Diagram of connections and operation of Thompson's 

recording wattmeter. 

and is connected up to a small commuitator composed of 
silver bars. Two thin silver brushes toucJi this commuta- 
tor and carry the current to and from the armature. The 
torque on the motor is proportionial to the product of the 
current in the fields and armature. In well regulated sys- 
tems, the voltage supplied is so nearly constant tHiat the 
current in the armature is practically the same for any 
load. 



216 

It should be remarked that, in order i)0 reduce the 
current wasted in passing through the armature to the 
smallest possible amount, there is in series with the arma- 
ture a very large external resistance. The voltage supply 
being practically constant, the current through the arma- 
ture will also remain constant. The onl^' factor that varies 
much is the current in the field. Eddy currents are gener- 
ated in the copper disc by its motion between the poles of 
the permanent magnets, and doubling the speed doubles the 
voltage produced and therefore doubles the current or quad- 
ruples the watts lost in the disc. 

In order to make the instrument register correctly, the 
speed must be twice as great when 20 amperes are passing 
through the field as when only 10 amperes are passing 
through. 

Doubling the current through the field doubles the mag- 
netic field through which the armature revolves, and this 
doubles the torque on the armature. Doubling the speed 
doubles the current produced in the retarding disc, so that 
the increased torque is balanced by an equally increased 
resistance or counter torque in the disc. If the armature 
speed is doubled its counter electro-motive force will be 
quadrupled, because it is revolving at double speed in a 
field of double strength. 

Since in any case the counter electro-motive force is 
extremely small, the current passing through the armature 
is not varied appreciably by the variation in the counter 
electro-motive force. We have fhen, by dou'bllng the speed, 
quadrupled the watts lost in the revolving copper ring and 
at the same time have quadrupled the energy imparted to 
the armature by quadrupling its electro-motive force 



217 

against a constant current. Since these same relations al- 
ways hold, it is clear that the speed of the instrument will 
be always proportional to the current passing through it. 
Consideraition will show Ithat a change in the voltage While 
the current remains coonstan twill change the eounter electro- 
motive force of the armature and its speed in the same way 
that change of current does. 

If the voltage alone should change and the current be 
constant, the same relation is true. 'Suppose the voltage to 
be doubled; the current through the armature would be 
doubled and there wouild 'be twice the torque on the arma- 
ture. This double torque would produce double speed and 
consequently double counter E. M. F. acting against double 
current, or it would exert four times as much energy as at 
the lower speed. 

Thus, for either case of change of voltage or current 
the speed of rotation is a correct measure of the energy 
passing through it. 



QUESTIONS ON CHAPTEK XVIII. 



1. What does a common volt meter really measure? 

2. On wha't law does tlie accuracy of the common volt 
meter depend? 

3. If, m Fig. 68, thie righit-hand pole is nortlh, which 
way does the current flow through the right-hand side of 
the bobbin when the needle registers voltage? 

4. What makes the Weston volt meter dead beat? 

5. What is the object of the iron core between the 
poles of the horse-shoe magnet? 

6. "lYhen the meter registers the voltage and comes to 
rest, what two forces are equal? 

7. On what does the permanent accuracy of this meter 
depend? 

8. What is the difference between the Weston am- 
meter and volt meter? 

9. Describe the electrical connections in the ammeter. 

10. Describe the action of thie magnetic vane instru- 
ment. 

11. What is the objection to measuring instruments 
using soft iron? 

12. Wliy is the speed of the Thompson recording meter 
proportional to the watts in the circuit to which it is con- 
nected? 

13. If the voltage of the circuit supplying the current 
is constant, and the power required to rotate the copper 
disc is proportional to the square of the speed, why will 
doubling the current double the speed? 



CHAPTER XIX. 



ALTERxNATING CURRENTS. 



The currents thot have been previously considered in 
this work have been direct; that is, constantly flowing in 
one direction. An alternating current is one which changes 
its direction manj^ times every second; that is, the current 
flows first in one direction and then in the opposite, the 
time required for alternation or reversal varying from 1-50 
to 1-275 of a second. In the older lighting dynamos the 
number of alternations usually employed was from 250 to 
266 per second. Modern alternating current machinery op- 
erates from 50 to 125 alternations per second. 



♦ MAK. 




Figure 78 
Two successive alternations or one cycle. 



Fig. 78 is the diagram of two successive alternations in 
a circuit. Two successive alternations, such as shown in 
this figure, are called a period or a cycle. A two-pole ma- 
chine will produce one cycle every revolution. Fig. 79 



220 



shows a bi-polar dynamo with a single coil wound on it, 
with the two ends of the coil connected to a pair of rings on 
which brushes make contact. As this coil revolves between 
the poles of the dynamo there will be a certain E. M. F. 
produced at each point. The E. M. F. will be a maximum 
when the coil is horizontal and the plane of the coil and 
plane of the poles coincide. From this point on the volt- 
ao-e decreases graduailly until the coil is vertical, and at 
this point becomes zero. As the coil moves on voltage is 




Figure 79 
Alternating current produced in a bipolar field. 



again generated, but now in the opposite direction. When 
the coil reaches the horizontal position the voltage will be a 
negative maximum, which gradually diminishes until the 
coil has reached the vertical position again and the voltage 
sunk to zero. The voltage will now be produced in a posi- 
tive direction and again increased to a maximum. 



221 



A cycle is usually considered to begin at the point at 
which the voltage is at zero and at which the current which 
is to be generated in the next half revolution will be posi- 
tive. 

Fig. 80 shows a coil revolving in a uniform field. Such 
a coil will generate what is known as a sine wave; this is 
the form of the current wave that is sought in all power 
transmitting machinery. Ftig. 78 shows the sine wave. 




Figure 80 
Coll revolving in uniform field and producing a sine wave. 



The old Westinghouse alternating current dynamos used 
for lighting were run at 133 cycles per second. The Thomp- 
son-Houston were run at 125 cycles per second. Most of 
the modern alternating current machinery is run at 7,200 
alternations per minute, or 60 periods per second. The 
great plant at Niagara Falls, which transmits power to 
BufPalOj runs at 3,000 alternations per minute, or about 25 
per second. An ordinary alternating current is called a 
single phase current. Such a current as would be gener- 
ated in the mechanisan shown in Figs. 79 and 80 would be 
a single phase current. 



222 



A two-phase current is really not one current, but two 
separate currents produced from one d^-namo. One of these 
currents succeeds the other in such a way that when the 
first current is at a maximum the other current is at zero; 
in other words, they are a quarter cycle apart. 




Figure 81 
One current of a two phase current. 




■MAX. 



Figure 82 
The other current in a two phase current. 



Pig. 81 shows one of the current-s in a two-phase dy- 
namo; Fig. 82 shows the other. Fig. 83 sho'ws the two com- 
bined in one diagram. Fig. 84 shows a way in which a two- 
phase current may be taken from a direct current commu- 



223 



tator. It will be seen by an exainination of Fig. 84 that 
the two currents which are taken from the commutator of 
the two-polo dynamo are connected to bars which are 90 de- 
o-rees apart; thus w^hen the current in circuit No. 1 is at zero, 
the commutator bars to which it is attached are on a hori- 
zontal line and there is no difference of voltage between the 



♦ MA*. 



♦ MAX 




-MAX. -MAX 
Figure 83 
Diagram of two phase currents or Figures 81 and 82 on one diagram. 



^ ^.Kft. 



BRUSH 

RING 

INSULA 




Figure 84 

Method of producing two phase current from the commutator 

of a bipo«<tr armature. 



224 



two bars, and therefore there is no current in the circuit. 
The circuit No. 2 is attached to bars which are in a vertical 
line, and the voltage between these bars is at a maximum. 
Fig. 84 makes it clear why it is that the two currents in a 
two-phase circuit are said to- be 90 degrees apart. A three- 
phase current is one in which, there are three currents, but 
they can hardly be called three separate currents. If the 



♦MAX. ♦ 




I .^V I > 



•HAX 



Figure 85 
A diagram of the currents in a three phase line. 



three sliding rings shoAvn in Fig. 86 be connected to three 
commutator bars 120 degrees apart on the commutator of a 
two-pole dynamo, the current which is taken from these 
three sliding rings is a three-phase current, as 
shown in diagram in Fig. 85. Thus, if there 
were 36 bars in the commutator of a two-pole dynamo, one 
slide ring would be attached to commutator bar No. 1. The 
second slide ring will be attached to commutator bar No. 13 
and the third slide ring would be attached to commutator 
bar No. 25; or, each slide ring is attached to a point 1-3 the 
circumference of the commutator aw^ay from its neighbor. 
Since there are 360 degrees in a circle, these currents are 
•aid to be 120 degrees apart. If a two-phase current were 



V 



226 



to be taken from this same commutator, circuit No. 1 would 
be attached to bars Nos. 1 and 19; circuit No. 2 would be 
attached to bars Nos. 10 and 28. By a proper combination 
of two-phase or three-phase currents it is possible to pro- 
duce a revolving pole. By placing inside of the applaratus 
which produces this revolving pole a short circuited arma- 
ture, this wall be dragged around by the revolv- 
ing pole in the same way that a short circuited armature 
in a direct current machine would be dragged around if the 
fields were revolved about such an armature. Such a ma- 
chine is called an induction motor. 



IM A A f 








Figure 86 

IMethod of producing three phase current from the commutatoi 
of a bipolar armature. 



The great advantage that alternating currents possess 
over direct currents is that they can be transformed from a 
low voltage and a large current to a high voltage, and small 
current without any moving mechanism, or vice versa. 



t26 

Alternating current is usually generated for lighting 
purposes in a dynamo at from 1,000 to 2,000 volts. A small 
cjrrent at this high voltage will transmit a large number 
of wratts, and only small wires will be needed to transmit 
this small current; one ampere, for instance, of this cur- 
rent at 1,000 volts is received in the primary coil of a trans- 
former, which changes it into 10 amperes at 100 volts, or 20 
amperes at 50 volts, depending upon the winding of the 
transformer. This low voltage current is distributed 




Figure 87 
Diagram of alternating current transformer. 

through the building to be lighted and operates 20 incan- 
descent lamps. Fig. 87 is a diagram of a transformer; P ia 
the primary coil which receives the high voltage current, S 
is the secondary coil which delivers the low voltage current, 
I is an iron core passing through both coils. According 
to Lentz's law, current will be generated in the secondary 
coil in opposition to that of the primary. The number of 
turns on the primary and on the secondary coils is in the 
ratio of their voltages. Thus, if there are 100 turns on the 
primary coil and it is deigned to receive current at 1,000 



227 



volts, there \vill be five turns on the secondary coil if it is 
desired to have it deliver current at 50 volts. 

The transformers are connected in parallel across the 
main circuit and the self-induction of the primary coil pre- 
vents excessive current from fiowing* through it when 
the secondary circuit is open. Thus, suppose current is 
siupplied at 125 periods per second and that there are 100 
turns on the transformer and that 2,000,000 lines flow 
throiigh the core of the transformer on an average. A 
little study will show that the voltage produced in a coil 
having 100 turns placed around this iron core would be 

100x125x4x2,000,000 



100,000,000 

Solving this equatioai, we find that there will be 1,000 volts 
produced in such a coil. 

If 1,000 volts would be produced in a separate coll, 
there must be the same voltag-e produced in the coil which 
is attached to the 1,000 volt line wires. In this coil the 
voltage will appear as counter electro-motive force oppos- 
ing the voltage of the anain circuit. This E. M. F. is al- 
most precisely equaljto the E. M. F. on the large line wires, 
and, in fact, the only current that leaks through the pri- 
mai-y coil is just enough to- produce ampere turns suffi- 
cient to cause 2,000,000 magnetic lines to flow through the 
iron core of the transformer. 

When the secondary circuit is closed, however, the cur- 
rent in it tends to de-magnetize the iron core, because, ac- 
cording to Lentz's law, it flows in the opposite direction 
to that in the primary coil. There will be, therefore, a 
certain number of counter miagnetizing turns due to the 
current in the secondary coil, and there must be always 



228 

juat enough more mag-netizing' turns in the primary coil to 
overcome the de-magnetizing turns in the secondary coil 
and still force the magnetic flux through the iron core, and 
so produce the counter E. M. F. in its own coils sufficient 
to oppose the E. M. E. of the main line. 

It will be rioted that the transformer receives and de- 
livers the same number of watts, but that this number of 
watts may be made up volts and amperes in almost any 
ratio that we please by properly choosing the number of 
turns on the two coils. The Ruhmkorff coil is an example 
of this, in which a battery current of a few volts and eight 
or ten amperes is transformed into an exceedingly small 
current, but having a voltage of hundreds of thousands of 
volts. It is to be kept in mind that the battery current is 
interrupted or, in effect, made alternating by the circuit 
breaker on the coif. The alternating current system of 
transmitting power is without doubt destined to come into 
very extensive use on account of the ease of transformation 
with a transformer without any moving parts and on ac- 
count of the cheapness of the line over which the power 
can be efficiently transmitted after being transformed with 
such little expense. Lines are in use in this country in 
which power is transmitted 40 miles at a pressure of 40,000 
volts. In an experimental plant in Germany power was 
transmitted 130 miles with a loss in the line amounting to 
only 13 per cent. Without doubt power electrically trans- 
mitted by alternating currents of high voltage is destined 
to play a very large part in the industrial development of 
this country. 



QUEST10:s'S ON CHAPTER XIX. 

1. What is an alternating current? 

2. How many alterna'tions per second were used in the 
older lig-hting systems? 

3. What is a period? 

4. A four-pole machine is running" 1,100 reTolutions 
per minute; if it is producing alternating current, how 
many cycles per second will this current have? 

5. How may an alternating current be produced from 
an ordinary direct current motor or dynamo? 

6. What is a sine wave? 

7. >What is a single phase alternating current? 

8. What is a two phase alternating current? 

9. If a two phase current is taken from a direct cur- 
rent two-pole dynamo, to what points on the commutaitor 
will the four rings be attached? 

10. ^Vhat is a three phase alternating current? 

11. How may a three phase current be produced from 
a direct current two-pole dynamo? 

12. Why are the currents of a two-phase current said 
to be 90 degrees apart, while the currents of a three-phase 
current are said to be 120 degrees apart? 

13. If possible, sketch the connections which would be 
necessary to produce a revolving pole with a two-phase cur- 
rent. 



230 



14. What advantages do alternating currents liave over 
direct currents? 

15. What is an alternating current transformer? 

16. What is the object of a transformer? 

17. How is current produced in the secondary coil 
from a primary coil with insulation of thousands of ohms 
between the two coils? 

18. Why will a transformer connected across a thou- 
sand-volt circuit and having a resistance of only one ohm 
allow only a small part of an ampere to pass? 

19. Why will the current in the primary coil increase 
when the resistance of the secondary circuit decreases? 

20. What is true of the watts received by the primary 
coil and the watts delivered by the secondary coil? 

21. WTiat is a Rhumkorff coil? 

22. Why is the alternating system of power transmis- 
sion rapidly coming into use? 



ANSWERS TO QUESTION'S ON CHAPTER J. 



1. Nothing of its ul'timate nature. 

2. They are probably better understood than the laws 
gpoverning heat land light. 

3. The operation of an hydraulic system. 

4. (a) The water pressure or head, (b) The amount 
of flow or number of gallons per minute, (c) The friction- 
al resistance of the pipes earrjdng the water. 

5. The volt. 

6. To one foot of head or pressure. 

7. The -ampere. 

8. The ohm. 

9. Amperes equal volts divided by ohms. 

10. Ohm's law is only the application of a general law 
to electrical action. The flow of heat through a wall is an 
example. 

11. About two. 

12. Usually 110. 

13. (a) One-half ampere, (b) From six and a half to 
ten. 

14. One ohm. 

15. Loss of pressure between boiler and engine in 
Bteam pipes. 



232 

16. On .the amount of fluid carried itbrongh Hhe pipe 
and on the straight ness and geoeral character of the pipe 
line. 

17. To tihe dj-^namo. 

18. To be filled in by student. 

IP. Upon the amount of cnrrenit transmitted and on 
the resistance of the wire. 

20. Draw a diagram and compare with Fig. 4. 
23. From 95 to 98 per cent. 

22. It is the loss of ^oltiage due to the resistance of the 
A' ires over which the current mu^t travel. 

23. The use of wires of such size that tOie loss of volt- 
age shall be practically zero. 

24. On account of the great size of conductors needed 
and the consequent expense. 

25. To select wire of such size thait t(he lamps shall at 
all times receive the same voltage. 

26. See text, page 8. 

27. No. (2). 

28. Write Out and compare with text. 

29. Four volts. 

30. Such a circuit would require 800 feet of No. 0000 
wire. 

31. i^ifty lamperes. 

32. .077 ohms. 

33. 108 volt48. 



233 

34. 12,100. 

35. Aboii't two voTts. 

36. Wire twice as Large as No. 0000. 

37. So as to reduce 'the drop to as small an amoun't as 
possible. 

38. $806.00. 

39. When only a few lamps are burning on a distant 
circuit, the voltage on this circuit is practically that of 
the dynamo, and tends to burn ouit the lamps. 

40. Table 2, page 16. 

41. At least 50 volts. 

42. Through the raiils and ground. 

43. Because the copper used in bonding 'the track is 
not nearly so great in amount as that required by the trol- 
ley wires and feeder. 

44. 2.59 times the size of a No. 0000 wire. 

45. $1,900.00. 

125 

46. x500 equals 833. 

75 

47. $1,141.00. 

48. No. 1 lor No. 0. 

49. Sucfh a system would leave the trolley wire discon- 
nected near the power house. Power would be supplied to 
the line from the dynamos by feed wires connected at a 
distance from the power start! on. 



234 

50. By the constaiift potentiaJ and constant current 
systems. 

51. For operatdng »the older arc lamp syst-ems. 

52. Each device for receiving electricity ds exposed to 
the siame eledtro-motive force. 

5H. Each device far receiving electricity must carry the 
same current. 

54. From 9^^ to 10 amperes. 

55. About 6l^ amperes. 

56. The resistatnce of the wire in ohms equals 10 8-10 
times tihe length in feett divided by the square of the diam- 
eter of the wire in tbousandlths of an inch. 



ANSWERS TO QUESTIONS IN CHAPTjiiR II, 

1. Galvani and Volta. 

2. Write the answer and compare with the text. 

3. From the negative plate through the outside circuit 
to the positive plate. 

4. The chemical action of the electrolite upon the posi- 
tive plate. 

5. The counter electro-motive force caused by the pro- 
duction on the negative plate of some gas, usually hydrogen. 

6. The positive element is the one on which the elec- 
trolite acts cheraioally; the negative element Is the remain- 
ing one upon which the electrolite has less or no chemical 
action. 

7. The terminal on the negative plate from which the 
current flows into the outside circuit. 

8. Platinum, carbon and silver. 

9. Because zinc and carbon are farther apart in the 
electro-chemical series than zinc and copper. 

10. Both mechanical and chemical means are employed. 
The mechanical means consists of blowing air or some other 
gas across the negative plate, or of providing numerous 
small points from which the gases may escape. 

11. Write the answer and compare with text. 

12. They cost too much. 



236 

13. Write description of Jablockoff battery and com- 
pare with text. 

14. Write description of plunge battery and compare 
with text. 

15. It should be amalgamated 

16. Directly proportional. 

17. An instrument in which the amount of current that 
has passed in a given time is measured by the amount of de- 
composition effected. 

18. Write answer and compare with text. 

19. An anode is the plate or electrode by which cur- 
rent enters the solution. A cathode is the plate or electrode 
by which current leaves the solution. 

20. With it. 

21. Write answer and compare with text, 

ELECTRO-PLATING. 

1. Metal is taken from the anode and deposited in a 
thin even layer on the cathode or work to be plated. 

2. See text. 

3. On the ampere hours or on tTie amount of current 
flowing multiplied by the length of time it flows. 

4. The work is burned. 

5. Yes. See text. 



237 

STORAGE BATTERIES. 

1. A storage batttery is one in iwhich electrical energ'y 
is consumed in producing chemical change and which will 
return the energy so stored as electrical energy upon de- 
mand. 

2. See text. 

3. It does not polarize, has a very low resistance, and 
<io is capable of producing heavy discharges, and has a high- 
er voltage than most primary batteries. 

4. For running horseless ciarriaiges and electric launch- 
es, and for absorbing the energy of a dynamo or circuit at 
times of light load and restoring it at times of heavy load. 
A battery may be very advantageously placed at or near the 
end of a long feeder line, so as to make the current that 
flows over the line nearly constant. 



ANSWERS TO QUESTIONS ON CHAPTER III. 



1. It is magnetized. 

2. A small magnet is supported in such a manner 
as to be free to turn in a horizontal plane. 

3. A north pole is one that points to the geographical 
north. A south pole is one 'that points to the geographical 
south. 

4. The region of magnetic influence surrounding the 
poles of a magnet. 

5. From the north pole into the air into the south 
pole and through the iron to the north pole. 

6. The figure formed usually by iron filings in a field 
of magnetic force, showing the direction and intensity of 
magnetic force. 

7. It is much more concentrated than that of a bar 
magnet. 

8. See text. 

9. The circular and concentric lines surrounding a 
wire carrying a current. 

10. The same as between the direction of rotation of a 
righl hand screw and its direction of motion forward or 
backward. 

11. Up. 

12. South. 

13. North. 



^9 

14. A piece of mag-netic metal around which a current 
is circula-ting. 

15. See text. 

16. That end of an electro-magnet around which the 
current circulates in the direction of motion of the hands of 
a watch, as seen by the observer, is the south pole. 

17. Yes. The lines of force flowing from the electro- 
magnet may be considered as the sum of the magnetic 
whirls of the wires which surround the core. 

18. A coil of wire in which a current flows. It is a 
weak magnet. 

19. An electro-magnet without a metallic or iron core 
would be a helix. 

20. Tt experiences a mechanical force that pulls it side- 
ways across the magnetic lines. 

21. Current and field "in proper relation are supplied 
and motion results. 

22. Motion and magnetic field properly related are sup- 
plied and electro-motive force which may produce a current 
is the result. 

23. Thumb, first and second fingers of the right hand 
are extended at right angles to each other, and point in the 
directions respectively of motion, lines and current. 

24. Extend the thumb, first and second fingers of the 
left hand at right angles to each other, and they will point 
respectively in the directions of motion, ISnes and current. 

25. Because the direction of lines would be reversed 
without reversing anything else. 



240 

26 The wire on top moves in one direction, the wire on 
the bottom in the opposite direction, both of which tend to 
produce rotation in one direction. 

27. Current will tend to flow from Hhe top to the bot- 
tom of the wheel. 

28. Current will flow^ in the direction oi the hands of 
a watCih, as seen by the observer on the south side of the 
loop. 

29. Current will flow from east to west. 

30. Current flows away from the observer. 

31. About 1-10 of a pound per foot. 

32. 100,000,000. 

33. Yes. To provide sufficient friction between the 
wire and the armature core to prevent the Wares moving 
from the mechanical force exerted between the current in 
the wire and the magnetic field. 



AiNSWERS TO QUESTIONS ON CHAPTER IV. 



1. On the a.mper« turns. 

2. Yes. The relation between magnetic flux, ampere 
turns or mag-netic motive force and magTietic reluctance is 
the same as that between current, electro-motive force and 
electric resistance, as given by Ohm's law. 

3. The flux corresiponds to the current, the ampere 
turns or magne^ac motive force to the electro-motive force. 

4. Directly proportional <to the leng*th of the circuit 
and inversely proportional to its area. 

5. It multiplies the number of lines passing- throug^h 
the helix. 

6. Because all the magnetic lines must pass throug-h 
the center of 'the helix amd the area is restricted while the 
return path for the mag-netic lines outside the helix is 
practically unlimited. 

7. Flux equals ampere turns x area divided by leng*th 

1425x7.07 

X.3132 equals equals 5850. 

5y2X.3132 



21 
8. — X5850 equals 8190. 
15 



r 



242 

9. The multiplj'^ing power of a magnetic metal for 
magnetic lines. 

10. Because the permeahility is not constant. 

11. When it is carrying a great many magnetic lines. 

12. It is said to be saturated. 

13. In order to reduce the magnetic reluctance suffi- 
ciently to allow enough lines of force to pass to produce 
the proper E. M. F. 

14. By comparing the number of magnetic lines that 
actually do flow through iron with the number that would 
flow through the same space occupied by air. 

15. They are about equal. 

16. It is a representatdon of one sample, but only ap- 
proximately represents the class. 

17. Wrought iron has about twice the permeability of 
cast iron. 

18. Because the permeability of each part is different 
and it is easier to get the desired result by making the 
separate calculations. 

19. 3371. 

20. A. t. in adr gap 2595 

A. t. in body of teeth 100 

A. t. in neck of teeth 103 

A. t. in armature 495 

A. t. in pole piece 22 

A. t. in yoke 56 



243 

21. A. t. in air g-ap, 2770 
A. t. in body of teeth, 240 
A. t. in neck of teeth, 200 
A. t. in armature, 38 
A. t. in pole piece, 49 
A. t. in yoke, 105 

22. Because the larger number of ampere turns is ex- 
pended in the air gap and an error in this calculation would 
make a great difference in the result, while the same error 
in the calculation of the yoke, for instance, would not make 
nearly the same difference. 

23. About one-half. 

I,000,000x37.68x.3132 

24. A. t. equals equals 3970. 

9.62x309 

25. Nickel and cobalt. 

26. No. 

27. One in whicli the wire is wound on the surface. 

28. They give mechanical support to the armature 
wires and greatly reduce the reluctance of the air gap. 

29. The lines tend to pass from the surface of tthe p©le 
piece in tufts or bunches. 

30. 12x(.310-f .062)x5 equals 22.32. 

5000xlx.3132 

31. A. t. equals equlals 783, 

%x4 



244 



32. From 125,000 to 140,000 lines per square inch. 

33. It will reduce the flux six or eigfht per cent. The 
exact amount of reduction could only be determined by 
making several g-u esses and figuring oult eaoh one. If we 
assume that it will decrease the flux 6%, figure out how 
many a. t. would be required in the imagnetic circuit for 
this number of lines, and, if nolt right, make a second or 
third. 

34. Because the permeability of tbe air gap while greait 
is constant, while the permeability of the iron part of the 
circuit depends very greatly on the amount of flux. 

35. Because it is practically impossible to obtain exact- 
ly correct permeability values. 



#" 



ANSWERS TO QUESTIONS ON CHAPTER V. 



1. One of the results of the flow of magnetic lines of 
force, usually exerted across an air gap between two pieces 
of iron. 

2. About 1,000 pounds per square inch. 

3. Because it increases the amount of flux across the 
air gap and does not produce enough to saturate the iron 
parts of the circuit. 

4. Because the pull is proportional to the square of the 
number of lines per square inch, and if the same flux can be 
crowded down to a small area the total pull will be increased 

5. The magnet will be one foot in diameter if It is to 
be as light as possible, for a given area of contact can be 
secured with less* weight in a magnet of large diameter than 
with one of small diameter. The magnet is required (to ex- 
ert a pressure of 3,000 pounds. Assuming a pressure of 270 
pounds per square inch, the contact area will be 11.11 or 5.55 
on each side. The cross section of the naagnetic circuit will 

14 
be 5.55 X — equals 7.77, 

10 

Assuming a coil 1 inch by 2 inches, as in Fig. 33b, the ouit- 
side diameter of magnet will be 12 inches. The 'thickness 
of the wall will be .2 inch to give an area of 7.77 square 
inches in each side. The outside diameter of inner ring will 
be 9.6, and the inner waill will be .26 thick. 



246 

^. Area of magnetic circui/t equalls 2x2x.7854 equals 3.14. 
Assume 100 turns on each coil: 33,000 lines must flow per 
square inch. 

104,720x2x.3132 

A. t. equals — equals 21,000. 

3.14 

Amperes in each coil equals 105. 

7. Annuljlir, as shown in Fig. 33a. 

8. Sectional <area of ma-gnet equals 5.8 square inches, 
assuming a pull of 270 pounds per square inch. Thickness 
of outside wall is aibout 1-3 of an inch. Assume coil to be 
3 2/. inch deep. Length of magnetic circuit equals about 614 
inches. A. t. equals 6i/,x25 equals 487. Add 300 a. t. for 
coni^tricted portion of the circuiit, or a. t. equals 787. 



ANSWERS TO QUESTIOlSrS ON CHAPTER VI. 



1. MagTietic lines that are produced but do not pass 
throiig*h that part of the circuit that they were intended to 
traverse. 

2. From 15 to 800 times better than air. 

3. By exposing as little pole surface as possible to the 
air and having* rounded corners on v^hat is exposed. 

4. Because the surface at full magnetic difference of 
potential exposed to the air is so great in the Edison and 
so small in the internal pole. 

5. About 8,800 tlhrough eacQi slot. 

6. About 64,000. 

7. Because iron conducts magnetic lines a few hundred 
times better than air and copper conducts electric current 
millions of times better than air. 

8. No; it only makes the magnet core and yoke heavier 
than they v^ould otherwise be. 

9. Magnetic leakage is apt tx) draw nails, oil cans, 
wrenches, etc., into the poles, when they may be entangled 
with the armature. 

10. Small magnetic leakage and the removal of sur- 
faces that would attract iron pieces from much chance of 
drawing anything into the armature. 

11. The number of lines that pass through the field 
magnet core divided by the number th|at pass through the 
armature. 



ANSWERS TO QUESTIONS ON jOHABTER VTI. 

1. See formulaetNos. (8), (9)tand (10) in t€xt. 

2. 1746. 

3. 6x500 equals 4000. 

^1/2x746 

4. equals amperes equals 37.3. 

110 

5. .0663. 

6. 134. 

7. 4.97 per cent. 

8. No. 

32 

9. — amperes. 
55 

10. On 110 volts 6.782, on 220 voJts 3.391, on 500 volts 
1.492, on 1000 volts .746, on 10,000 volts .0746. 

11. On no volts 9.09, on 220 volts 4.545, 'on 500 volts 2, 
on 1,000 volts 3, on 10,000 volts .1. 

12. Because the voltage is higher and the current lower 
than if the dynamos were in parallel. 

13. More economical because the voltage would be still 
further raised and the current reduced in the same ratio. 

14. Because (it permits of the use of a oheap line with 
only small loss of power. 



249 

15. It could not be aooomplislied witih 250 volts. 

16. It could not 'be aooomplished with '500 watts. About 
95 per oen't of the 100 horse power would be losit in the line 
at 1,000 volts; 49 volts or 180 waltts or l^ of 1 per cent, with 
20,000 volts. 

17. Because with the same copper cost the amount or 
weight used is the same, and if this is run two inches in- 
stead of one, the resistance oreach mile is doubled and the 
miles of line are doubled, and therefore the resistance quad- 
rupled. 

18. As the square of the voltage. 

19. The distance varies directly as the voltage. 

20. 0000 wire is the nearest standard size, and this will 
cost $506.40. 

21. Three No. 000 wires can be used, and this 'will cost 
$1,140.75. 

22. The drop specified in <this question should have been 
omitted, and then the current would be 123.3. 

23. Because the armature generates voltage and when 
it is in operation there is no way of measuring what is used 
in the armature resistance. Therefore the other two for- 
mulae that contain the voltage lost cannot be easily applied. 



ANSWERS TO QUESTIONS ON CHAPTER VIII. 



1. To know the length of the average turn. 

2. See text. 

3. 4129. 

4. No. 17. 

5. 32,400. 

6. Because the number of a. t. is increased with the 
same size of wire if it is small in diameter, and a small wire 
and small power will therefore produce more a. t. if of 
small circumference than if of large. 

7. In order to have section enough of iron to allow the 
magnetic flux to pass. 

8. Because an increase in th.e amount at 'tihe wire de- 
creases the current that flows through the coil in the same 
proportion thaJt it increases the turns. 

9. Yes. A heavy coil requires only a small amount of 
current to produce a given magnetizing power, and there- 
fore runs cooler. 

10. For 6-volt plaiting dynamo No. 6 vdre gives 2788. 
For 110-volt dynamo No. 18 gives 3150. 

For 220-volt dynamo No. 21 givets 3165. 
For 500-vK>lt dynam'o No. 24 gives 3612. 

11. For plating dynamo No. 6 wire requires 121/2 poundjS. 
For 110-volt dyniimo No. 18 requires 16 pounds. 
For 220-volt dynamo No. 21 requires 16 pountds. 
For 500-vcilt dynamo No. 24 requires 201/2 pounds. 



251 

12. One watt per square inch. 

13. If thicker than this the heat from the inside layers 
of wire has difficulty in getting away to the outside surface. 

14. .21 of 1 per cent, per degree F. 

15. Divide the number of amperes that a coil of one 
pound will pass by the number of amperes it is desired to 
have the finished coil pass, and the result is the desired 
weight. 

16. iSizo of wire required is No. SO. Weight of wire re- 
quired is 14 pounds per coil. 

17. 20.9 pounds of No. 21 wire gives 3,600 -a. t. at full 
pressure of 250 volts and a heat loss of i/g watt per sq. in. 

18. Divide number of ampere turns required by num- 
ber of amperes that will flow, and the result is the number 
of turns. 

19. It decrease the current by increasing the resist- 
ance throug'h the coil and so decreases the power lost in 
the coil. 

2i). It increases the resistance and so increases the 
power lost. 



ANSWERS TO QUESTIONS IN CHAPTER IX. 



1. 100,000,000. 

2. See text. 

3. It is a device by which direct current is obtained 
from an armature in the wire of which the current is alter- 
nating*. 

4. Because there must be two paths for the passage of 
the current through a direct current armature, and each 
path contains only half the a.mount of wire that is used on 
the whole armature. 

5. 120 volts. 1,500 revolutions. 

6. See text. 

7. 1,388,889. 

8. The best winding will 'be two parallel of .072 wire, 
and the resi^tamce of the armature will be .0816 ohms. Di- 
mensions of arm'aiture will be found in Fig. 29. 

9. If the motor is of the same size it will only be neces- 
sary to double the number of 'turns on the armature. 

10. Twice as many turns are required on a gramme 
ring armature as ooi a drum armature. 

11. In the gramme ring method of winding, adjacent 
coils are at a small difference of potential, and Jt is easy to 
repair a coil if one gets out of order. 

12. 223.2 square inches. 

13. The number of wires will be doubled, "tihe sejctianal 
area will be halved, thus quadrupling the resistiance. 



ANSWEKS TO QUESTIONS IN CHAPTER X. 



1. The electro-motive force produ-ced in an electrical 
device which tends to reduce the current which the primary 
electro-motive force would rend to produce. 

2. No. 

3. Because tlie counter electro-motive force is very 
nearly equal to the primary elec'tro-motive force. 

4. By an application of formula (14), 

5. 925.8 revolutions per minute. 

6. 3,174,600. 

7. Because as the temperature X3f the fields rise the 
resistance rises and the ampere turns decrease, consequently 
the flux decreases and the speed increases in the same ratio 
as the flux decreases. 

8. The Pafton street *car was an example of this, in 
which a gas engine drove a dynamo which on light loads 
and down grades charged la storage (battery, while on heavy 
loads and up grades it became a motor and absorbed power 
from the storage battery. 

9. The fact that the flux through the armature is con- 
stant and the voltage lost dne to the resisance of the arma- 
ture is very small, even at heavy load. 

10. Because the voltage lost in a large armature is rela- 
tively less for the same heating than in a smaller armature. 

11. Because it decreases the counter electro-motive 
force by decreasing the effective flux through the armature. 



264 

12. Volts lost m armature with one ampere equal .08 
volts. Volts lost in armature with 30 amperes equal 2.4 
volts. The drop in speed in per cent, will be 2.4 divided by 
79.92 equals 3 per cent. 

13. Because the ampere turns on the field coil of a 
series motor, and therefore the magnetic flux through the 
armature, depend npon the load on the armature. 

14. Because the flux through the field magnets tends 
to become constant a-fter th^ iron becomes saturated. 

15. The magnetic flux across an air g*ap is strictly pro- 
portional to the ampere turns expended in the air gap, and 
if the iron is unsaturated at the highest voltage, practically 
all the ampere turns will be expended in the air gap and the 
flux through the armature will be proportional to the volt- 
age, thus making the speed constant. 

16. In the same way that the speed of a series motor 
does, but not in the same degree. There will be an upper 
limit set to the speed on account of the flux produced by 
the shunt coil. 

17. The torque of an armature is proportfonal to the 
product of the current and magnetic flux through it. When 
the iron is unsaturated the flux through the armature will 
be doubled by doubling the current, and the double flux, 
acting on the double current, produces four times the torque. 

18. To the current passing through the armature. 

19. On a constant potentiial circuit with no load on the 
armature the increasing speed produces an increasing coun- 
ter electro-motive force, which reduces the current (tihrough 
the fields, thus reducing the flux through the armature, 
which thus t^nds to further increase the speed. The oon- 



255 



at ant speed is finally reached on laccount of the mechamoal 
power required to rotate the armature at suoh a hig-h rate 
of speed. On a constant current circuit the counter elec- 
tro-motive force tends "to become equal to the primary elec- 
tro-m'otive force. 

20. In two ways: Firsty by reducing the ampere turns 
on the field by means of a centrifug-al device; land second, 
hy decreasing- the effective flux through the armature by 
rocking the brushes. 



ANSWERS TO QUESTIONS ON CHAPTE'R XI, 



1. Molecular friction. 

2. An alternating cnrremt would set up changes in the 
iirection of the magnetic flux, and therefore produce hys- 
teresis, while a direct current would not. 

3. Because at the same numOber of revolutioins per min- 
ute there are twice as many reversals of m<aignetism in a 
four-pole motor armature as in a two-pole. 

4. The direction of the magnetism is reversed in the 
iron core of an airmature in passing from a south pole to a 
north pole. 

5. Currents other 'than the m<ain current set up in an 
armature due to its rotation, which produce wasteful heat. 

6. In the same direction that the currents flow in the 
wires. 

7. To prevent eddy currents. 

8. To prevent eddy currents in the copper, which would 
be formed in the large solid conductor. 

9. With a Y&ry short air gap there will be tufts of lines 
flowing from the pole pieces to the armature teeth, and 
therefore the flux of lines from a small given area of sur- 
face on the pole piece changes and so produces currents in 
accordance with Lcntz law. 

10. The permeability of steel pole pieces is so much 
greater than that of cast iron that it permtts of this tufting 
to a much greater extent than cast iron. 



.V 



257 

11. The armature in Figf. 35 is four-pole and there will 
be two currents in one direction across it and two currents 
in the opposite direction. The voltage of one of these cur- 
rents will be .48, or practically 14 of a volt; the resistance 
will be 1.6 of an ohm in the whole ix:^ath of one of these cur- 
ren-ts. The watts lost will be .143 of a watt. The power 
lost will be % of a watt. 

12. No. 

13. To more perfectly insulate the larmature discs 
from each other than is possible by means of the oxide on 
the surface of each disc. 

14. The heating of the armature chars this paper in- 
sulation, and so loosens the armature discs on the shaft 
between the end plates. 

15. As the square of the speed. 



ANSWERS TO QUESTIONS ON CHAPTER XII. 

1. The action of the armature as a mag'net due to the 
current which it generates passing around it. 

2. On Vie amount o-f current delivered "by the armature. 

3. In a general way it is magnetized ait right angles to 
the fields. 

4. Because this pole piece is of opposite polarity to the 
pole produced in the armature, While the pole piece whioh 
the armature is approaching is of the same polarity as the 
armature, and there is consequently (attraction between the 
first two and repulsion bet-ween the last two. 

5. The movement of the brushes gives a component of 
the armature reaction, whi<ili tends to increase or decrease 
the flux produced by the field coils. 

6. In order to stop the sparking the brushes must be 
rocked in such a direction that the armature reaction has a 
component which opposes the flux produced by the field 
coils. 

7. They would have to be rocked backward, in a direc- 
tion opposite to that of rotation, and this would produce 
severe sparking, 

8. In constant current dynamos. 

9. By rocking the brushes into various positions which 
controls the effect of the armature reaction in reducing the 
flux produced by the field coils, and so controls the voltage 
produced by the dynamo. 



269 

10. By reducing the current through the field coils and 
so weakening the flux, and consequently the voltage ipro- 
duced. This effect is greatly assisrted by the effect of arma- 
ture reaction aoid by rocking the brushes. 

11. They should be setiorward in the direction ol rota- 
tion, whifeh will usually cause severe sparking. 

12. Not more than half the ampere turns in the field 
coil. 

13. A gramme ring armature has twice as many turns 
as a drum armature, in order to produce the same voltage; 
therefore this form of armiature has a great armature reac- 
tion with a given current. Armature reaction is necessary 
in a constant current machine and should be avoided as 
much as possible in a consitant potential m'aehine. Another 
reason 2s that it is easier to insulate successfully a gramme 
ring armature for the high voltages produced in arc ma- 
chines than a dram armature. 

14. The field is made multi-polar. 

15. A four-pole machine would have half the ampere 
turns on each armature pole and the same number of am- 
pere turns in the air gap on each field pole if the same 
voltage is to be produced. Therefore the armature reaction 
will be decreased by half. 



ANSWERS TO QUESTIONS ON CHAPTER XIII. 

1. It is reversed. 

2. Half the total armature current. 

3. Chiefly on the field iu whic*h the coil is moving at 
the time, also on the resistance of leads and brushes. 

4. To reduce the current in the short circuited coil to 0. 

5. If the short circuited coil carries one-half the total 
armature current at the moment it ceases to be short cir- 
cuited, perfect comimutation will have -been effected. 

G. To retard the change of current in the short cir- 
cuited coil and so to produce sparking. 

7. None. 

8. Because in a dynamo rocking the brushes forward 
brings the short circuited coil into a magnetic field, that 
tends to reverse the direction of current in the short cir- 
cuited coil from what it was before it w^as short circuited, 
while in a motor the reverse is true. 

9. No. 

10. The production of over one-half the total armature 
current in the short circuited coil in the same direction that 
current flows in it after the coil leaves the brush. 

11. Rock them a long distance forward. 

12. The resistance between brush and commutator. 



k 



261 



13. It tends to cause the current to pass from the 
brush to the commutaitor evenly all over the brush. 

J 4. Over-commutaition is only possible where current 
is flowing" in oppos/ition to\the main current in one of the 
leads. 

15. On account of their resistance they tend to make 
the currenit enter the commutator evenly over the whole 
surface of the bruish. 

16. The g-reater resistance of the carbon brush pro- 
duces more heat than the copper brush wibh a giiven cur- 
rent. 

17. It will stop it enitirely. 

18. Becaoise its resistance is very much ihig-her. 

19. It allows time for the voltag*e to overcome the self- 
induction of the coil to be coimmutated. 

20. See text. 

21. The arc "that 'is formed between bar and brush 
melts the edge of the copper bar and it appears as a fi-^e 
liake of copper dusit. 

22. It musrt: be very low in order to avoid sparking, 

23. It shows that the commutaition produced on ac- 
count of the resistance of the brush is of much more im- 
portance in perfect oommutation than that produced by 
the magnetic field. 



J 



ANSWERS TO QUESTIONS IN CHAPTER XIV 



1. As a conductor in which E. M. F. is produced; sec- 
ond, as a conductor to carry the current to magnetize the 
fields. 

2. A circle surrounds the greatest area with the least 
length. 

3. It reduces the leakage surfaces. 

4. It must all flow in the same direction. 

5. Because the N. and S. poles are 90 degrees apart. 

6. 36 degrees for 36 degrees is 1-10 of the circumfer- 
ence of a circle, and current must flow in opposite direc- 
tions in zones 36 degrees wide. 

7. In order that the mechanical force shall be exerted 
in all the wires under the tw^o poles in the same directions 
as explained in chapter IV. 

8. 500 volts as a maximum. 

9. About 15.6 volts for both third and fourth and eley- 
enth and twelfth. 

10. The full voltage on the armature. 

11. One in which there is small difference of potential 
between coils in the same layer and the full difference of 
potential or voltage between the two layers. 

12. One in which each coil occupies the full depth of 
the winding on the armature and in which there is a maxi- 
mum difference of potential between coils of the same layer. 



k 



263 

13. By carrying the leads or connection's from the ar- 
ma»ture winding spirally around the armature the desired 
distjance. 

14. A wave winding is one in which it is possible to 
Lise two brushes on an armature for a four^ole machine 
without cross connecting the commutator. Under the same 
circumsitances a lap winding would require four ^brushes. 

15. Better magnetic TDalance in a unsymmetrical field 
and half the number of turns of wire. 

16. Because the magnet poles are 60 degrees apart. 

17. The positive brushes would be at degree, 120 de- 
grees and 240 degrees. The negative brushes would be at 
60 degrees, 180 degrees and 300 degrees. With a wave- 
wound armatu)re it is necessary to use only one positive and 
one negative brush, and these may be selected on opposite 
sides of the commutator if desired. 

18. 216. 

19. 108. 

20. The wave-wound armature will have four times the 
resistance. 

21. By cross connecting the commutator or connecting 
opposite bars on the commutator to each other. 

22. The wave-wound armatiire will operate just as if 
the armature w^as central. In the lap-wound armature one 
of the circuits will produce a higher voltage than 
others, and therefore tends to produce local currents in 
the armature. 

23. It cannot be connected symmetrically to the com- 
mutator. 



J 



264 

2 . Diagram, Fig". 88. 

25. A dynamo which has both series and shunt coils. 

26. To produce a machine which will produce a con- 
stant voltage on a variable load. 

27. The speed drops with increased load; volts lost in 
the armature drop, the armature reaction decreases the to- 
tal flux. These three causes decrease the voltage on the 
fields and therefore the ampere turns on the magnet. 

28. 4,200. 

29. A compound wound motor has ^the chiara-cteristics 
of both the series and shunt motors, ihe series winding 
making the speed variations greater than with the plain 
shunt motor. 

30. A compound wound motor will not spark cm over- 
load and has a greater torque with the same current than 
a plain shunt wound motor. 

31. At 500 volts the magnetic circuit is nearly satu- 
rated, and tbe increase in the ampere turns due to fhe 
series coil does not produce a proportional increase in the 
flux, while at 250 volts it does. 



^ 



ANSWERS TO QUESTIONS ON CHAPTER XV. 

\ 

1. It causes self-excitation. 

2. No. 

3. Reversing the connections causes the current due 
to the residual ma.gnetism to flow 'around the magnets in 
such a way as to decrease the residual magnetism instead 
of increase it. 

4. From two to five per cent. 

5. The saturation of the iron in the magnets. 

6. It w^ould rise to an infinite voltage or until gome 
part broke down. 

7. Connections between field and armature should be 
reversed. 

8. By bringing the macihine up to speed, measuring 
the voltage due to residual magnetism with a mili volt me- 
ter, then making the connection with the field magnet coil 
and noting whether the voltage rises or falls when this con- 
nection is made. 

9. As the load begins to come on the voltage will fall 
very rapidly. 

10. Moving the rheosta»t arm increases or decreases the 
resistance in the »hunt circuit. This changes the current 
through the shiint coil, which changes the ampere turns on 
the magnetizing circuit, and therefore the flux and voltage. 

11. The arc obtained by suddenly opening a field cir- 
cuit. 



266 



12. 6,750 volts. 

13. 36,000. 

14. So that the circuit can never be entirely opened. 

15. In order that the possibility of a field discharge 
niay be avoided. 

16. The ends of the sh.un»t coil are always connected by 
the resistance in the starting* box and the armature. 

17. To insert the resistance of the starting box in series 
with the armature to avoid sudden overload on the arma- 
ture vrhen the current returns. 

18. With Q series and shunt winding opposing each 
other. See text. 



ANSWERS TO QUESTIONS ON CHAPTER XVI. 



1. A break in the armature winding which prevents the 
passage of the armature current. 

2. By severe arcing on the commutator. 

3. By connecting together the two commutator bars 
between which the arc occurs. 

4. A connection in the armature or commutator which 
allows a local current to flow. 

5. 2,750 amperes. 

6. By heating the short circuited coil. 

7. It will completely short circuit the "armature, and 
it will refuse to generate as a dynamo. 

8. It will run only a half revolution at a time. 

9. Imperfect contact between brushes and commutator. 

10. 'Continual contact and a constant pressure between 
brushes and commutator. 

11. See text. 

12. The inertia does not allow the brush to move 
quickly. 

13. Heating and cutting the commutator and sparking. 

14. Forward in the direction of rotation. 

15. (Backward in the direction opposite to that. of rota- 
tion. 

16. Sec text. 

17. An unintentional connection between the armature 
or field winding and the frame. 



268 

18. To short circuit part of the armature or field wind- 
ing. 

19. Yes. Tf it has only a single ground. 

20. To remove the intentional ground. 

21. By making tests and finding the point of lowest 
voltage between the armature winding and the core. 

22. Tf the short circuit is between the series coil and 
that part of tihe shunt coil connected to the pole of the 
machine opposite to that to which the series coil is con- 
nected, the machine will be completely short circuited. 

23. By refusing to build up if it is a dynamo and by 
refusing to carry a heavy load with an ordinary current if 
a motor. 

24. By short circuiting one coil after another and mak- 
insr a test each time until the field circuit as a whole is 
closed. 

25. To decrease its magnetizing power and cause it to 
ran cooler. 

26. Because in the field ctoil the current is caused to 
flow by an external voltage, and if the resistance decreases 
the voltage deicreases; while in the armature each turn 
produces a constant electro-imotive force which is inde- 
pendent of the resistance of the circuit. 

27. By causing four times the amount of heat io oe 
generated in the field c<oil that remains in good condition. 

28. It causes a machine to act as if the field circuit was 
open, if there are only two field coils. 

29. By winding more wire on each field call. 

30. The minute elongation of each tooth as it suddenly 
enters the magnetic field, 



ANSWERS TO QUESTIONS ON CHAPTER XVII. 



I. By the heat produced by the /passage of a cTirreait 
through the high resistance of a small carbon iilament. 

2j Primarily to keep the filament from being burned up. 

3. Because it is absolutely necessary to preserve the 
vacuum, and platinum is the only metal that contracts and 
expands at the same rate as glass. 

4. It must be constant. 

5. From 21/2 to 41/0. 

6. If one is paying for both lamps aind electricity and 
wants light, it will pay to remove the dim Kamps and replace 
them with new ones at such a time tha t the cost of current 
and lamps to .produce a given amount of light shall be a 
minimum. 

7. About 7000 degrees Fahrenheit. 

8. Between 1-4 and 1-5. 

9. Because the light is more diffused. 

10. The oxygen of the air is excluded from the ho* 
carbons. 

II. See text. 



ANSWBT^S TO QUESTIOT^S ON CHiAPTEK XVm. 

1. A current proportional to the voltage. 

2. Ohm's law. 

3. Down throug'h the plane of the paper. 

4. The eddy currents generated in the copper coil on 
wh'ch the wire carrying the current is wound. 

5. Magnetic field uniform. 

6. The mechanical force lacting on the wares carrying 
current and the reaction of the hair springs. 

7. On the constancy of the permanent magnet. 

8. A difference in the size of wire on the movable coil 
which in the ammeter is adapted to receive much larger cur- 
rents a I a correspondingly lower voltage. 

0. See text. 

10. See text. 

11. The error introduced by the hysteresis of the soft 



iron. 



12. 'Write answer and compare with text. 

13. Write answer and compaire with text. 



k 



ANSWERS TO QUESTIONS ON CHAPTER XIX. 



1. A current which is constantly reversing its direotion. 

2. From 12 to 16,000 per minute. 

3. The time required for two successive alternatioois. 

4. 36 2-3. 

5. By connecting a circuit to two rings att|aohed to op- 
posite points on a direct current bi-polar commutator. 

6. The form of alteimating current wave produced by 
a coil revolving in a uniform field. 

7. A single alternating current. 

8. Two alternating currants produced or used by the 
same machine in such relation to each other that w^hen one 
is zero the other is maximum. 

9. To four points 90 degrees apart. 

10. Three alternating currents having a certain rela- 
tion to each other set forth in answer to question 11. 

11. By taking current from three rings attached to 
three points on a two-pole direct current dynamo 120 de- 
grees apart. 

12. Because two-phase circuits are attaohed to points 
90 degrees apart on a direct current bi-polar commutlator, 
and to produce a three-phase to points 120 degrees apart. 

13. Fig. 86. 

14. The volts and amperes can be transformed by static 
apparatus. 



272 

15. A device of iron and copper by which electric energy 
is transferred from one circuit o another without metallic 
contact. 

16. To receive a small current at a hig-h voltage and 
produce a large current at a correspondingly lower volt|age, 
or vice versa. 

17. On account of .the magnetic flux which is common 
to both the primary and the secondary coils. 

18. The self-induction of the coil produces a counter 
electro-motive force, which is very nearly equal to the pri- 
mary electro-motive force. 

19. The ampere turns of the secondary coil oppose 
those of the primary, but the primary' coil must always 
have enough ampere turns to force sufficient maignetic flux 
around the circuit to keep up its counter electro-motive 
force. When the resistance in the secondary circuit de- 
creases, the current, by Ohm*s law, increases, and the cur- 
rent in the primary must correspondingly increase. 

20. They are practically equal. 

21. A transformer of special design which has a small 
number of turns on the primary and a very great number 
on the secondary. 

22. On account of the flexibility of transformation and 
simplicity and reliability of generators and motors. 



273 

TABLE XL 
TENSILE ST;ftENGTII OF COPPEB VvIRE. 





Breaking weight 
Pounds 




Breaking weight 
Pounds 


2^! 










Hard- 
drawn 


Annealed 


Hard- 
drawn 


Annealed 


0000 


8 310 


5 650 


9 


617 


349 


000 


6 580 


4 480 


10 


489 


277 


00 


5 226 


3 553 


11 


388 


219 





4 558 


2 818 


12 


307 


174 


1 


3 746 


2 234 


13 


244 


138 


2 


3 127 


1 772 


14 


193 


109* 


3 


2 480 


1 405 


15 


153 


87 


4 


1 967 


1 114 


16 


133 


69 


5 


1 559 


883 


17 


97 


55 


6 


1 237 


700 


18 


77 


43 


7 


980 


555 


19 


61 


34 


8 


778 


440 


20 


48 


27 



The strength of soft copper wire varies from 32 000 to 36 000 pounds 
per square inch, and of hard copper wire from 45 000 to 68 000 pounds per 
square inch, according to the degree of hardness. 

The above table is calculated for 34 600 pounds for soft wire and 
60 000 pounds for hard wire, except for some of the larger sizes, where 
the breaking weight per squar© inch is taken at 50 000 pounds for 
000,000 and 00,55 000 for 0, and 57 000 pounds for 1. 



TABLE XII. 

CIRCUMFERENCES OF CIRCLES. 

ADVANCING BY TENTHS. 



Diam. 


.0 


.1 


.2 


.3 


.4 


.5 


.6 


.7 


.8 


.9 


Diam. 





.00 


.31 


.62 


.94 


1.25 


1.57 


1.88 


2.19 


2.51 


2.82 





1 


3.14 


3.45 


3.77 


4.08 


4.39 


4.71 


5.02 


5.34 


5.65 


5.61 


1 


2 


6.28 


6.59 


6.91 


7.22 


7.53 


7.85 


8.16 


8.48 


8.79 


9.11 


2 


3 


9.42 


9.74 


10.05 


10.36 


10.68 


10.99 


11.30 


11.62 


11.93 


12.25 


3 


4 


12.56 


12.88 


13.19 


13.50 


13.82 


14.13 


14.45 


14.76 


15.08 


15.39 


4 


5 


15.70 


16.02 


16.33 


16.65 


16.96 


17.27 


17.59 


17.90 


18.22 


18.53 


5 


6 


18.84 


19.16 


19.47 


19.79 


20.10 


20.42 


20.73 


21.04 


21.36 


21.67 


6 


7 


21.99 


22.30 


22.61 


22.93 


23.24 


23.56 


23.87 


24.19 


24 50 


24.81 


7 


8 


25.13 


25.44 


25.76 


26.07 


26.38 


26.70 


27.01 


27.33 


27.64 


27.96 


8 


9 


28.27 


28.58 


28.90 


29.21 


29.53 


29.84 


30.15 


30.47 


30.78 


31.10 


9 


10 


31.41 


31.73 


32.04 


32.35 


32.67 


32.98 


33.30 


33.61 


33.92 


34.24 


10 


11 


34.55 


3487 


35.18 


35.50 


35^1 


36.12 


36.44 


36.75 


37.07 


37.38 


11 


12 


37.69 


38.01 


38.32 


38.64 


38.95 


39.27 


39.58 


39.89 


40.21 


40.52 


12 


13 


40.84 


41.15 


41.46 


41.78 


42.09 


42.41 


42.72 


43.03 


43.35 


43.66 


13 


14 


43.98 


44.29 


44.61 


44.92 


45.23 


45.55 


45.86 


46 18 


46.49 


46.80 


14 


15 


47.12 


47.43 


47.75 


48.06 


48.38 


48.69 


49.00 


49.32 


49.63 


49.95 


15 


16 


50.26 


50.57 


50.89 


51.20 


51.52 


51.83 


52.15 


52.46 


52.78 


53.09 


16 


17 


53.40 


53.72 


54.03 


54.35 


54.65 


54.97 


55.29 


55.60 


55.92 


56.23 


17 


18 


56.54 


56.86 


57.17 


57.49 


57.80 


58.11 


58 43 


58.74 


59.06 


59.37 


18 


19 


59.69 


60.00 


60.31 


60.63 


60.94 


61.26 


61.57 


6188 


62.20 


62.51 


19 


20 


62.83 


63.14 


63.46 


63.77 


64.08 


64.40 


64.71 


65.03 


65.34 


65 65 


20 


21 


65.97 


66.28 


66.60 


66.91 


67.22 


67.54 


67.85 


68.17 


68.48 


68.80 


21 


22 


69.11 


69.42 


69.74 


70.05 


70.37 


70.66 


71.00 


7131 


71.62 


71.94 


22 


23 


72.25 


72.57 


72.88 


73.19 


73.51 


73.82 


74.14 


74.45 


74.76 


75.08 


23 


24 


75.39 


75.71 


76.02 


76.34 


76.65 


76.96 


77.28 


77.59 


77.91 


78.22 


24 


25 


78.54 


78.85 


79.16 


79.48 


79.79 


80.11 


80.42 


80.73 


81.05 


81.36 


25 


26 


81.68 


81.99 


82.30 


82.62 


82.93 


83.25 


83.56 


83.88 


84.19 


84.50 


26 


27 


84.82 


85.13 


85.45 


85.76 


86.07 


86.39 


86.70 


87.02 


87.33 


87.65 


27 


28 


87.96 


88.27 


88.59 


88.90 


89.22 


89.53 


89.84 


90.16 


90.47 


90.79 


28 


29 


91.10 


91.42 


91.73 


92.04 


92.36 


92.67 


92.99 


93.30 


93 61 


93.93 


29 


30 


94.24 


94.56 


94.87 


95.19 


95.50 


95.81 


96.13 


96.44 


96.76 


97.07 


30 


31 


97.38 


97.70 


98.01 


98.33 


98 64 


98.96 


99.27 


99.58 


99.90 


100.2 


31 


32 


100.5 


100.8 


101.1 


101.4 


101.7 


102.1 


102.4 


102.7 


lOb.O 


103.3 


32 


33 


103.6 


103.9 


104.3 


104 6 


104.9 


105.2 


105.5 


105.8 


106.1 


106.5 


33 


34 


106.8 


107.1 


107.4 


107.7 


108.0 


108.3 


108.6 


109.0 


109.3 


109.6 


34 


35 


109.9 


110.2 


110.5 


110.8 


111.2 


111.5 


111.8 


112.1 


112.4 


112.7 


35 


36 


113.0 


113.4 


113.7 


114.0 


114.3 


114.6 


114.9 


115.2 


115 6 


115.9 


36 


37 


116.2 


116.5 


116.8 


117.1 


117.4 


117.8 


118.1 


118 4 


118.7 


119.0 


37 


38 


119.3 


119.6 


120.0 


120.3 


120.6 


120.9 


121.2 


1215 


121.8 


122.2 


38 


39 


122.5 


122.8 


123.1 


123.4 


123.7 


124.0 


124.4 


124.7 


125.0 


125.3 


39 


40 


125.6 


125.9 


126.2 


126.6 


126.9 


127.2 


127.5 


127.8 


1281 


128.4 


40 


41 


128.8 


129.1 


129.4 


129 7 


130.0 


130.3 


130.6 


131.0 


131.3 


131.6 


41 


42 


131.9 


1132 .2 


132 5 


132.8 


133.2 


133.5 


133 8 


134.1 


134 4 


1^4.7 


42 


43 


la^.o 


135.4 


135.7 


136.0 


136.8 


136.6 


136 9 


137.2 


137.6 


137.9 


43 


44 


138.2 


138.5 


138.8 


139.1 


139.4 


139.8 


140.1 


140.4 


140 7 


141.0 


44 


45 


141.3 


141.6 


142.0 


142.3 


142.6 


142.9 


143.2 


143.5 


143.9 


144.2 


45 


46 


144.5 


144.8 


145.1 


145.4 


145.7 


146.0 


146.3 


146.7 


147 


147.3 


46 


47 


147.6 


147.9 


148.3 


148.6 


148.9 


149.2 


149.5 


149.8 


150.1 


150.4 


47 


48 


150.7 


151.1 


151.4 


151.7 


152.0 


152.3 


152.6 


152 9 


153.3 


153.6 


48 


49 


153.9 


154.2 


154.5 


154.8 


155.1 


155.5 


155.8 


156.1 


156.4 


156.7 


49 


50 


157.0 


157.3 


157.7 


1.58.0 


158.3 


158.6 


158.9 


159.2 


)f.9.5 


1.59.9 


50 



H 
W 

o 

M 

o 

< 



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r-> vHi-^TSf-liH 1-1 rl 1-1 FH CM CM CM CM CM ?5 



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QOi^'»rtMoi o»o^'?oc<i oJodocQcc ad^r;^5C5'<* t-* m' od m* •^* 

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iOCD«Ot-C^ t-QOOSOSO O»-l»^(MC0 CO -^ ift »ft CO t-OOOOOSO 

C<lSt-§Q C<1t^C-00 00 C<I 'f*^ W OO 1-^ 1-1 go (M « 

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lOCOCDcDt- t^oooooso O»Hi-iC<l?0 CC 'r^ Lf5 »rt CO t-c^ao050 

cooscorci-H oooco _ 

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lO aiai'^irici t-^ co co' t-' t4 »fteqoso5 c<it-^c<iooo 

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iftiOCOCOt- t-OOX'OSO Oi-!i-lC^?3 CQ'+'^iOCO t-c-caooso 

t-OOi-l-^OO COOO»rtC<IQ 

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iftiftCOCOt- t-0030OiO5 Oi-li-tC<I5<l CC-'^'^iftCO COt^aOOiO 

NCOMQOia C<Ii-(QOtH 

oa-^t-co?3 t-opoDi-Hco c^ioOiHcooi "»**cO'^qco coo^tft-^ 

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tr^ainaOha '^'•^'cooshh* oododosTH coi-Hoioo'od q'-^'oscoio 

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iftiTJCOCOtr- t-0000O5Oi 00'^C<1C<1 CC -^ -^ iTJ CO COt^OOOiOS 

1-t tH iH i-( tH t-( 1-H 1-H rl tH rl i-( i-^ t-i »H 

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W coo (MO •rt<00 05 0CO Oil— ^OOi« cqcO»«CCC-^ CDi-iC<I05iH 

cciftoJ-^iH O5oio*"^*a6 "^'-ci c<i* CO »« oijcc^iTHiH cct^c^'ooc^ 

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IftiftCOCOt- C-3000O5OS OOt^OJC^J OC-t-^LCCO COt-OO^Oi 

§]t-OoSi-l W«^M'«*< i-ICDOCt-CO COt-'«*0OQ t-'^*'t-C^CO 

1-iOiocDco kftCQcocOi-j c<iQqooqc^^ i-jcqt-?tco cc c-^ «o i-< c*5 

oii-H-^05 CO •^'•^iftodco oscdcdcdoi c<iy5ir:^^ cooi-^i-Joi 

CC30C<ICDiH COi-icbi-tt- C^IOO-^QCO COCiCOCCQ C--^C<IQt- 

iCtrtcocot- t-ooooosos ooi-i^oa ccco'tutco «Dt^X)Cfeos 

cgO»«OOa6 -^oCOit-C^l "^COC^C^ICO OiOep»rtiH COCOOkftCD 

OaOT-jOift CO N "^^ C<) CO iOOOC-^OS t-^p»'<*»ft '^.^.'~1'^.^ 

iftcoo»ftiH oiosQcdt^ cdi-ioQc<i cos^oct-'c^ osco'c-^cdiH 

CCt-Cv]&TH lftQcO»^cp ^OC^QCO C^3 Oi krt C<J 05 CO -^ i-H 05 tr- 

»rtir;co«>t- t-oDooosos oOi-i^Sco cocc^w-ric cot-oooooi 

OCOCOthQ OiOSQC<l»« _ 

COirtirtCMCO CO'+QC<li-( t-T-dHOS"^ »rt-^OCOCO Q ■<* CO -^ Q 

05 »rt t- »ft 5q c-^ c^i CO OS ih oq c<i i^_ ta co c<i -^ n i« •** en os »ft c-^ K 

Q c<i »fl o* CD •^* ^' ifi t-* c<i C-* ir; ^" •^* cp o »« c<j o* Q ^ "^' O? »«* co 

«t-'^CDO iftQkTSOCO ^C-COOS»rt C^JCJQtrtOJCfe CO ?t Q 5q CO 

ut»r:coc43C- t-ooxiosos oOi-" — cm co'.C'«t»r5»o cot— ooooot 



SSS^^ 5??;5??^i5? ^?5?8^5 :55S55i3 S§q;2852 



277 



TABLE XIV. 



AREAS OE SMALL CIRCLES. 



ADVANCING BY HUNDREDTHS, 



1 


.00 


.01 

.000078 


.02 
.00031 


,03 


.04 


.05 
.00196 


06 


.07 


.08 


.09 


eO 


.0 


.0007 


.00125 


.00283 


.00385 


.00503 


.00636 


.1 


.0078 


.0095 


.00113 


.0133 


.0154 


.0177 


.0201 


.0227 


.0255 


.0283 


.2 


.0314 


.03464 


.038 


,0415 


.0452 


.0491 


.0531 


.0572 


.0616 


.0666 


.3 


.0706 


.0755 


.0804 


.0855 


.0908 


.0962 


.1018 


.1075 


.1134 


.1195 


.4 


.1256 


.132 


.1385 


.1442 


.1520 


.1590 


.1662 


.1735 


.181 


.1886 


.5 


.1963 


.2043 


.2124 


.2206 


.2290 


.2376 


.2463 


.2552 


.2642 


.2734 


.6 


.2827 


.2922 


.3014 


.3117 


.3217 


.3318 


.3421 


.3526 


.3632 


3739 


.7 


.3848 


.3959 


.4071 


.4185 


.4301 


.4418 


.4536 


.4657 


.4778 


.4902 


.8 


.5026 


.5153 


.5281 


.5411 


.5542 


.5674 


.5809 


.5945 


.6082 


.6221 


.9 


.6362 


.6504 


.6648 


.6793 


.694 


.7088 


.7238 


.739 


.7543 


.7698 



TABLE XV. 



pricp: list of copper magnet wire. 



Size, 
B. &S. 
Gauge 


1 Cotton 


snk 


Single 


Double 


Single 


Double 


16 






1 1 12 


$ 1 53 


17 







1 12 


1 53 


18 








1 15 


1 57 


19 






1 15 


1 57 


20 


$ 60 


$ 74 


1 18 


1 61 


21 


70 


• 88 


120 


1 63 


22 


76 


95 


1 30 


1 76 


23 


83 


1 05 


1 42 


1 93 


24 


90 


1 14 


1 56 


2 13 


25 


100 


1 27 


1 81 


248 


26 


1 10 


1 38 


2 10 


2 88 


27 


1 25 


1 57 


2 25 


3 07 


28 


1 35 


1 69 


238 


3 27 


29 


1.50 


1 89 


2 75 


3 76 


30 


1 65 


2 07 


2 95 


4 02 


31 


1 80 


2 23 


3 25 


4 40 


32 


1 95 


2 28 


3 45 


4 53 


33 


240 


■ 2 85 


3 90 


5 10 


34 


2 85 


3 42 


4 10 


5 30 


35 


3 25 


3 88 


5 85 


7 78 


36 


4 37 


4 93 


7 00 ■ 


888 


37 


6 75 


7 25 


11 00 


13 63 


38 


9 00 


9 50 


13 00 


14 50 


39 


UOO 


12 00 


15 00 


18 00 


40 


13 00 


15 00 


20 00 


2300 



279 

TABLE XVI. 

SPECIFIC GKAVITIBS OF METALS. 



Names of metals 


Specific 
gravity 


Weights 

per cubic 

foot 


Specific 
heat 


Melting 

point in 

degrees 

Fahr- 

enheit 


Aluminum, cast 

" hammered. . . 

Antimony 

Arsenic 


2.5 
2 67 
6.702 
5.763 
4. 

9822 

8.604 
1.566 
73 
8.6 

8.895 
8.878 
8.788^ 
8.946 
8.958 

8 931 
8.914 
19.258 
7.483 
7.79 

7.85 
11.445 

2.24 

6.9 
13.568 

7.832 
20.3 

.855 
10.522 

.972 

2.504 
7.291 
6.861 


156 06 
166 67 
418.37 
359.76 
249.7 

613.14 
537.1 
97.76 
455.7 
536.86 

555.27 
554.21 
548.59 
558.47 
559.25 

557.52 
556.46 
1 202.18 
467.18 
486.29 

490.03 
714.45 
139.83 
430 73 

846.98 

488.91 
1 267.22 

54. 
656.84 

60.68 

156.31 
455.14 
428.29 


.214 3 

056 8 
.081 4 

.030 8 
.056 7 

'.'.'/.'.'. 
.107 

.095 1 





.032 i 

.13 

.113 

.116 
.031 4 
.249 9 
.114 
.031 9 

.109 1 
.032 4 
.169 6 
.057 
.293 4 

■.656"2 
.095 5 


"sio. 

365 


Barium 




Bismuth 

Cadmium 

Calcium 


497. 
500. 


Chromium 




Cobalt 

Copper 

•' rolled 

" cast 

'• drawn 

" hammered 

" pressed 

'* electrolytic 

Gold 

Iron, bar 

'* wrought 


1 996. 

2616. 

2 786. 

3 286 


Steel 

Lead 


3 286. 
612 


Magnesium 




Manganese 


3 000 


Mercury 


3« 


Nickel 

Platinum 


280 0. 
.S2M fi 


Potassium 


136 


Silver 

Sodium 


1 873. 
194 


Strontium 




Tin 

Zinc 


442. 
773 







(T 





WIRE GAUGES IN MILLS. 






TABLE XVIL 








Brown 


Birmingham 




Numbers 


Roebling 


& 


or 


New British 






Sharpe 


Stubs 


standard 


000 000 


460. 






464. 


00 000 


430. 







432. 


0000 


393. 


460 


454!" 


400. 


000 


362. 


409.6 


425. 


372. 


00 


331. 


364.8 


380. 


348. 





307. 


324.9 


340. 


324. 


1 


283. 


289 3 


300. 


300. 


2 


263. 


257.6 


284. 


276. 


3 


244. 


229.4 


259. 


252. 


4 


225. 


204.3 


238. 


232. 


5 


207. 


181.9 


220. 


212. 


6 


192. 


162. 


203. 


192. 


7 


177. 


144.3 


180. 


176. 


8 


162. 


128.5 


165. 


160. 


9 


148. 


114.4 


148. 


144. 


10 


135. 


101.9 


134. 


128. 


11 


120. 


90.74 


120. 


116. 


12 


105. 


80.81 


109. 


104. 


13 


92. 


71.96 


95. 


92. 


14 


80. 


64.08 


83. 


80. 


15 


72. 


57.07 


72. 


72. 


16 


63. 


50 82 


65. 


64. 


17 


54. 


45 26 


58. 


56. 


18 


47. 


40.3 


49. 


48. 


19 


41. 


35.89 


42. 


40. 


20 


35. 


31.96 


35. 


36. 


21 


32. 


28.46 


32. 


32. 


22 


28. 


25.35 


28. 


28. 


23 


25. 


22.57 


25. 


24. 


24 


23. 


20.1 


22. 


22. 


25 


20. 


17.9 


20. 


20. 


26 


18. 


15.94 


18. 


18. 


27 


17. 


14.2 


16. 


16.4 


28 


16. 


12.64 


14. 


14.8 


29 


15. 


11.26 


13. 


13.6 


30 


14. 


10.03 


12. 


12.4 


31 


13.5 


8.93 


10. 


11.6 


32 


13. 


7.95 


9. 


10.8 


^i 


11. 


7.08 


8. 


10. 


34 


10. 


6.3 


7. 


9.2 


35 


9.5 


5.62 


5. 


8.4 


36 


9. 


5. 


4. 


7.6 



■1 



281 

TABLE XVII. 

DECIMAL EQUIVALENTS OF PARTS OF AN INOH. 



8thg 



% equals .125 
.250 
.375 
.500 
.625 
.750 
.875 



% 

7Z 



16ths 



T^ equals .0625 

7 
TV 

w 

ii 



.1875 
.3125 
.4375 
.5625 
.6875 
.8125 
.9385 



32ds 



3^y equals .03125 
i^ " .09375 
3»5 *' .15625. 
.21875 
.28125 
.34375 
.40625 
.46875 
.53125 
.59375 
.65625 
.71875 
.78125 
.84375 
.90625 
.96875 



H 
hi 

§1 
§^ 
§§ 



64ths 



^ equals 


.015625 


b\ " 


.046875 


A " 


.078125 


B^^ " 


.109375 


b\ " 


.140625 


^i " 


.171875 


H '' 


.203125 


M " 


,234375 


iJ ** 


.265625 


11 " 


.296875 


li " 


.328125 


II " 


.359375 


II " 


.390625 


II '' 


.421875 


II " 


.453125 


II " 


.484375 


If " 


.515625 


II " 


.546875 


il " 


.578125 


II " 


.609375 


II " 


.640625 


Jl " 


.671875 


11 " 


.703125 


II " 


.734375 


II " 


.765625 


li '' 


.796875 


II " 


.828125 


II " 


.859375 


II " 


.890625 


II " 


.921875 


II " 


.953125 


II " 


.984375 



ELECTRICAL WORDS, TERMS AXD PHRASES DEFINED 



A. C. — Abbreviation for alternatina^ current. 

ACCELERATION— The rate of change of speed or velocity. 

ACCUMULATOR, A SECONDARY OR STORAGE CELL- 
Two inert plates partially surrounded by a fluid inca- 
pable of acting chemically on either of them until after 
the passage of an electric current, when they become 
capable of furnishing an independent electric current. 

.AFFINITY, CHEMICAT.— Atomic attraction. 

The force which causes atoms to unite and form chem- 
ical molecules. 

ALARM, BURGLAR — A device, generally electric, for auto- 
matically announcing the opening of a door, window, 
closet, drawer, or safe, or the passage of a person 
through a hallway, or on a stairway, 

ALARM, ELECTRIC— An automatic device by which atten- 
tion is called to the occurrence of certain events. 

ALLOY — A combination, or mixture, of two or more metal- 
lic substances. 

ALLOY, GERMAN SILVER— An alloy employed for the 
v/ires of resistance coils, consisting of 60 parts of cop- 
per, 25 of zinc, and 25 of nickel. 



AMP 284 

.VLPHABET, TELEGRAPHIC: MORSE'S- Various group- 
ing's of dots and dashes, which represent the letters of 
the alphabet or other signs. 

ALTERNATIONS— Changes in the direction of a current in 

a circuit. 

A current that changes its direction 300 times per sec- 
ond is said to possess 300 alternations per second. 
ALTERNATIONS, COMPLETE— A change in the direction 

of a current in a circuit from its former direction and 

back again to that direction. A complete to-and-fro 

change. 

Complete alternations are sometimes indicated by the 

sym]>oL o^ 
ALTERNATOR — A name commonly given to an alternate 

current dynamo. 
AMALGAM — A combination or mixture of a metal with 

mercury. 
AMBER — A resinous substance, generally of a transparent, 

yellow color. 
AMMETER- -A form of galvanometer in which the value of 

the current is measured directly in amperes. 
AMMETER, MAGNETIC-VANE— An ammeter in which the 

strength of a magnetic field produced by the current 

that is to be measured is determined by the repulsion 

exerted between a fixed and movable iron vane, placed 

^*n said field and magnetized thereby. 
AMxMETER, PERMANENT-MAGNET— A form of ammeter 

in which a magnetic needle is moved against the field 

of a permanent magnet by the field of the current it Ts 

measuring. 
AMPERAGE — The number of amperes passing in a given 

circuit. 



285 ARC 

AMPERE— The practical unit of electric current. 

Such a current as would pass with an electromotive 
force of one volt through a circuit whose resistance is 
equal to one ohm. 

A current of such strength as would deposit .005034 
grain of copper per second. 

AMPERE-TURN— (See Turn, Ampere). 

ANION — The electro-negative radical of a molecule. 

An anion is that group of atoms of an electrically de- 
composed of electrolyzed molecule which appears at 
the anode. 

ANNUNCIATOR, ELECTRO-MAGNETIC— An electric de- 
vice for automatically indicating the points or places 
at which one or more electric contacts have been closed. 

ANNUNCIATOR, HOTEL — An annunciator connected with 
the different rooms of a hotel. 

ANODE — The conductor or plate of a decomposition cell 
connected with the positive terminal of a battery, or 
other electric source. 

That terminal of an electric source out of which the 
current flows into the liquid of a decomposition cell. 

ARC— A voltaic arc. 

ARC — To form a voltaic arc. 

ARC, ALTERNATING — A voltaic arc formed by means of 
an alternating current. 

ARC, HISSING OF — A hissing sound attending the forma- 
tion of voltaic arcs when the carbons are too near to- 
gether. 



ARM 286 

ARC, VOLTAIC— The source of lig-ht of the electric arc 
lamp. 

ARM BRIDGE— One of the sections in a Wheatstone bridge 
for necessary resistance. 

ARM-CROSS — A transversie piece attached to a pole for the 

support of wires, 
ARM, ROCKER —An arm on which the brushes of a dynamo 

or motor are mounted for the purpose of shifting their 

position on the commutator. 

ARMATURE— A mass of iron or other magnetizable mate- 
rial placed on or near 1:he pole or poJes of a magnet. 

ARMATURE, RI-POLAR— An armature of a dynamo-elec- 
tric machine the polarity of which is reversed twice in 
every rcA^olution through the field of the machine. 

ARMATURE, DRUM— An armature of a dynamo-electric 
machine, in which the armature coils are wound longi- 
tudinally over the surface of a cylinder or drum. 

AR^IATURE, DYXAMO-ELECTRIC MACHINE— That part 
of a dynamo-electric machine in w^hich the differences 
of potential which cause the useful currents are gen- 
erated. 

ARMATURE, POLARIZED— An armature which possesses 
a polarit3^ independent of that imparted b}^ the magnet 
pole near which it is placed. 

ARMATLH^E, RING — A dynamo-electric machine armature, 
the coils of which are wound on a ring-shaped core. 

ARMATURE, SPHERICAL— A dynamo-electric machine ar- 
mature, the coils of which are wound on a spherical 
Iron core. 



387 BAG 

ARRESTEPi, LIGIITNTNG— -A device by means of which 
the apparatus placed in any electric circuit is protected 
from the destructive effects of a flash or bolt of light- 
ninor. 

ASTATIC — Possessing no directive power. 

Usually applied to a magnetic or electro-magnetic 
device which is free from any tendency to take a defi- 
nite position on account of the earth's magnetism. 

ATMOSPHERE, AN— A unit of gas or fluid pressure equal 
to about 15 pounds to the square inch. 

ATTRACTION, MAGNETIC— The mutual attraction exert- 
ed between unlike magnet poles. 

AURORA BOREALIS— The Northern Light. Luminous 
sheets, columns, arches, or pillars of pale, flashing light, 
generally of a red color, seen in the northern heavens. 

AUTOMATIC CONTACT BREAKER— (See Contact Breaker, 
Automatic). 

AUTOMATIC CUT-OUT— (See Cut-Out, Automatic). 

B 

B — A contraction used in mathematical writings for the 
internal magnetization, or the magnetic induction, or 
the number of lines of force per squaire inch or per 
square centimetre in the magDctized material. 

B. A. OHM— (See Ohm, P. A.) 

B. W. G. — .\ contraction for Birmingham wire gauge. 

BACK ELECTROMOTIVE FORCE— (See Force, Electromo- 
tive, Bacl<). 



BAT 288 

BALANCE, COULOMB'S TORSION— An apparatus to meas- 
ure the force of electric or magnetic repulsion between 
two similarly charg'ed bodies, or between two similar 
magnet poles, by opposing- to such force the torsion of 
a thin wire. 

The two forces balance each other; hence the origin 
of the name. 

B.^ LANCE, INDUCTION, HUGHES'— An apparatus for the 
detection of \he presence of a metallic or conducting* 
substance by the aid pf induced electric currents. 

BALLS, PITH — Two balls of pith, suspended by conducting 
threads of cotton to insulated conductors, employed to 
show^ the electrification of the same by their mutual 
repulsion. 

BARS, BUS— Omnibus bars. (See Bars, Omnibus). 

BARS, OMNIBUS — Main conductors common to two or 
more dj^namos in an electrical generating- plant. 

The terms bus and omnibus bars refer to the fact 
that the entire or whole current is carried by them. 

BATH, COPPER — An electrolytic bath containing a readily 
electrolyzable solution of a copper salt, and a copper 
plate acting as the anode, and placed in the liquid near 
the object to be electro-plated, which forms the kath- 
ode. 

BATH, ELECTRO-PLATING -Tanks containing- m.etallic 
solutions in w^hich articles are placed so as to be eloc- 
tro-j^lated. 

BATH, NICKEL — An electrolytic bath containing a readily 
electrolyzable salt of nickel, a plate of nickel acting as 
the anode of a battery and placed in the liquid near the 
object to be coated, which forms the kathode, 



^ 



2fi9 BAT 

BATTEKY, CLOSED-CIRCLTIT— A voltaic battery which 
may be kept constantly on closed-circuit without seri- 
ous polarization. 

BATTERY, ELECTRIC— A general term applied to the 
combination, as a single source, of a number of sepa- 
rate electric sources. 

BATTERY, GAS— A battery in which the voltaic elements 
are gases as distinguished from solids. 

BATTERY, LEYDEN JAR— The combination of a number 
of separate Leyden jars so as to act as one single jar. 

BATTERY, LOCiL— A voltaic battery used at a station on 
a telegraph line to operate the Morse sounder, or the 
registering or recording apparatus, at that point onl}'. 

B\TTERY, OPEN-CIRCIIIT- A voltaic battery which is 
normally on open circuit, and which is used continu- 
ously only for comparatively' small durations of time 
on closed-circuit. 

BATTERY, PIJLVGE— A number of separate voltaic cells 
connected so as to form a single cell or electric source, 
the plates of which are so supported on a horizontal 
bar as to be capable of being simultaneously placed 
in, or removed from, the exciting liquid. 

BATTERY, PRIMARY— The combination of a number of 
separate primary cells so as to form a single source. 

BATTERY, SECONDARY— The combination of a number 
of separate secondary or storage cells, so as to form a 
single electric source. 

BATTERY SOLUTION— (See Solution, Battery). 

BATTERY,' STORAGE— A number of separate storage cells 
connected so as to form a single electric source. 

BATTERY, VOLTAIC— The combination, as a single source, 
of a number of separate voltaic cells. 



BOM 200 

BELL MAG::^ET0 ELKCTKIG— a bell rung by the move- 
menft of the armature of an electro magnet. 

BELL, TELEPHONE-CALL— A call bell used to call a cor- 
respondent to the telephone. 

BI-POLAR— Having two poles. 

BL \STTNC, ELECTETC— The electric ignition of powder 
or other explosive material in a blast. 

BLOCK, BBANCH — A device employed in electric wiring 
for taking off a branch from a main circuit. 

BLOCK, EI^SE — A block containing a safety fuse or fuses 
for incandescent light circuits. 

BOABD, HANGEB— A form of board provided for the -eady 
placing' or removal of an arc lamp from a circuit. 

BOAKD, IVfTJLTTPLE SWITCH— A board to which the nu- 
merous circuits employed in systems of telegraph 3% 
telephonj^ annunciator or electric light and power cir- 
cuits are connected. 

BOAPiD, SWITCH— A board provided with a switch or 
switches, by means of w^hich electric circuits connected 
therewith may be opened, closed, or interchanged. 

BOBBIN. ELECTPiTC— An insulated coil of wire for an 
electro-magnet. 

BODY, ELECTRIC B-ESISTAXCE OF~The resistance of 
the hum»an body measured from hand to .hand varies 
from 3,000 ohms to 15,000 ohms. 

BOLO^rETEK — An apparatus devised by Langley for meas- 
uring small diflferences of temperature. 

BO^.fBAPDMEXT, MOLECULAR— The forcible rectilinear 
projection from the negative electrode, of the gaseous 
molecules of the residual atmospheres of exhausted ves- 
sels on the passage of electric discharges. 



i>91 BRI 

BORE, ARMATURE— The space provided between the pole 
pieces of a dynamo or motor for the rotation of the 
armature. 

BOX, DISTRTCT-CALL— A box by means of which an elec- 
tric signal is automatically sent over a telegraphic line 
and received by an electro-magnetic device at the other 
end o^ the line. 

BOX, FIRE-ALARM SIGNAL— A signal box provided for 
the purpose of automaticalh'' sending an alarm of fire. 

BOX, FUSE— The box in which the fuse-wire of a safety- 
fuse is placed. 

BOX, JUNCTION — A moisture-proof box provided in a sys- 
tem of underground conductors to leceive the termi- 
nals of the feeders, in which connection is made be- 
tween the feeders and the mains, and from which the 
current is distributed to the individual consumer. 

BOX, RESISTANCE — A box containing a number of sepa- 
rate coils of known resistances employed for determin- 
ing the value of an unknown resistance, and for other 
purposes. 

BRx^KE, ELECTRO-MAGNETIC- A brake for car wheels, 
the braking power for which is either derived entirely 
from electro-magnetism, or is thrown into action by 
electro-magnetic devices. 

BRAKE, PRONY — A mechanical device for measuring the 
power of a di'iving shaft. 

BRANCH-BLOCK— (See Block, Branch). 

BREAKER, CIRCUIT— Any device for breaking a circuit. 

BRIDGE-ARMS- (See Arms, Bridge or Balance). 



r 



BRU 292 

BRIDCxE, ELKCTPJC— A device for measurinjj the value of 
electric resistances. 

The electric bridg-e is also called the Electric V>alanc^. 

BPilDGE, MAGNETIC— An apparatus invented by Edison 
for measuring' mao-netic resistance, similar in principle 
to Wheatstone's electric bridg-e. 

BRUSH, mSCHARGE— (See "Discharo-e, Brush). 

BRUSH-HOLDERS FOR DYNAMO-ELECTRIC MACIIIN]:S 
— Devices for supporting- the eollectingf brushes of dy- 
namo-electric machines. 

BRUSH ROCKER— (See Rocker, Brush). 

BRUSHES, ADJUSTMENT OF DYN A MO-ELECT RrC MA- 
CHINES — Shifting the brushes into 1he required posi- 
tion on the commutator cylinder, either non-automatic- 
ally by hand, or automatically by the current itself. 

BRUSHES, CARBON, FOR ELECTRIC MOTORS— Plates of 
carbon for leadinsr current to electric motors. 
These are generally known simply as brushes. 

BRUSHES, LEAD OF— The angle through ^vhich the 
brushes of a dynamo-electric machine must be moved 
forward, or in the direction of rotation, in order to 
diminish sparking and to get the best output from the 
dynamo. 

BRUSHES OF DYNAMO-EIJXTRIC ]S1ACHLNE— Strips of 
metal, bundles of wire, slit plates of metal, or plates of 
carbon, that bear on the commutator C3^1inder of a 
dynamo-electric machine, and carry off the current 
generated. 



>^ 



jmmmm 



293 C. G. S. 

BUCKLING — Irregularities in ^he shape of the surfaces of 
the plates of storage cells, following a too rapid dis- 
charge. 

BUG — A term originally employed in quadruplex telegra- 
phy to designate any fault in the operation of the ap- 
paratus. 

BUNSEN VOLTAIC CELL— (See Cell ,Voltaic, Bunsen's). 

BUEGLAK ALAI^M ANNUNCIATOR— (See Annunciator, 
Burglar Alarm). 

BURNEK, AUTO.AIATIC-ELECTRIC— An electric device for 
both turning on the gas and lighting it. and turning it 
ofF, by alternately touching different buttons. 

BUS— A word generally used instead of omnibus. 

BUS-BARS- -rSee Bars, Bus). 

BUTTON, CARBON— A resistance of carbon in the form of 
a button. 

BUTTON, PL^SH — A device for closing an electric circuit by 
the movement of a button. 

BUZZER, ELECTRIC— A catl. not as loud as that of a bell, 
produced by a rapid automatic make-and-break. 



C — An abbreviation for centigrade. 

C — A contraction for current. 

C. C. — A contraction for cubic centimetre. 

C. G. S. UNITS — A contraction for centimetre-gramme-sec- 
ond units. 



CAL 



294 



C. P. — A contraction for candle power. 

CABLE — To send a telegraphic dispatch, by means of a 

cable. 
CABI>E, BIIXCHED — A cable containing" more than a single 

wire or conductor. 

CABLE, CAPACITY OF— The ability of a wire or cable to 
permit a certain quantity of electricity to be passed 
into it before acquiring a given ditt'erence of potential. 

CABLE, ELECTKIC— The combination of an extended 
length of one or more separately insulated electric con- 
ductors, covered externally with a metallic sheathing 
or armor. 

CABLE, SUBMAPJXE— A cable designed for use under 
water. 

CABTiEGR\M — A message received by means of a subma- 
rine telegrajjhic cable. 

CALIBRATE — To determine the absolute or relative value 
of the scale divisions, or of the indications of any elec- 
trical instrument, such as a galvanometer, electrome- 
ter ,voltameter, wattmeter, etc. 

CALL-BELL, MAGNETO-ELECTBIC— An electric call-bell 
operated by currents produced by the motion of a coil 
of wire before the poles of a permanent magnet. 

CALORIE, GREAT— The amount of heat required to raise 
the temperature of one kilogramme of water from 
degree C. to 1 degree C. 

CALORIE, S:NrALL— The amount of heat required to raise 
the temperature of one gramme of water from degree 
C. to 1 degree C. 



B 



295 CAB. 

CANDLE — The unit of photometric intensity. vSuch a liglit 
q^s would be produced by the consumption ot two grains 
of a standard candle per minute. 

CANDLE, JABLOCHKOFF— An electric arc light in vrhich 
the two carbon electrodes are placed parallel to each 
other and maintained a constant distance apart by 
means of a stieet of insulating material placed betv/een 
them. 

CANDLE-POWEK— (See Power, Candle). 

CAOUTCHOUC, OR INDIA-RUBBER— A resinous substance 
obtained from the milky juices of certain tropical trees. 

CAPACITY, ELECTROSTATIC— The quantity of electricity 
which must be imparted to a given body or con'hictor 
as a charge, in order to raise its potential a certain 
amount. 

CAPACITY, ELECTROSTATIC, UNIT OF— Such a capacity 
of a conductor or condenser that an electromotive force 
of one volt will charge it with a quantity of electricity 
equal to one coulomb. The farad. 

CAPACIl'Y, SPECIFrC INDUCTIVE— The ability ol a di- 
electric to permit induction to take place tnrough its 
mass, as comi)ared with the ability possessed by a mass 
of air of the same dimensions and thickness, under pre- 
cisely similar conditions. 

CARBON — An elementary substance which occurs naturally 
in three distinct allotropie forms, viz: charcoal, graph- 
ite and the diamond. 

CARBON POINTS— (See Points, Carbon). 



CAU 296 

CAEBOX TEANSMITTEK FOR TELEPHONES— (See 
Transmitter, Carbon, for Telephones). ^ 

CARBONING LAMPS— (See Lamps, Carboning). 

CARBOXJZE — To reduce a carbonizable material to carbon. 

CARBONS, ARTIFICIAL -Carbons obtained by the carboni- 
zation of a mixture of pulverized carbon with different 
carbonizable liquids. 

CARBOXS, CORED- -A cylindrical carbon electrode for an 
arc lamp that is molded around a central core of char- 
coal, or other softer carbon. 

CARBOXS, FLASTITXG PROCESS FOR— A process for im- 
proving- the electrical uniformity of the carbon conduc- 
tors employed In incandescent lighting, by the dejDosi- 
tion of carbon in their pores, and over their surfaces at 
those places where the electric resistance is relatively 
great. 

CARD, COMPASS — A card used in the mariner's compass, 
on which are marked the four cardinal points of the 
compass X, S, 1^ iind W, and these again divided into 
thirti^-two points called Rhumbs. 

CARDEW VOLTMETER- (See Voltmeter, Cardew). 

CATAPHORESIS — A term sometimes employed in place of 
electric osmose. (See Osmose, Electric). 

CATHODE — A term sometimes used instead of Kathode. 

CAUTERTZATI0X,1^.LECTR1C— Subjecting to cauterization 
by means cf a wire electrically heated. 



297 CEL 

CAUTERY, KLECTKIC— An instrument used for electric 
cauterization. Jn electro-therapeutics, the application 
of vaiioiisly shaped platinum wires heated to incan- 
descence by the electric current in place of a knife, for 
removing- diseased growths, or for stopping- hemor- 
rhages. 

CELL, ELECTEOLYTIC— A cell or vessel containing an 
electrolyte, in which electrolysis is carried on. 

CELT , POliOUS — A jar of unglazed earthenware, employed 
in double-ftuid voltaic cells, to keep the two liquids sep- 
arated. 

CELL, SECONDATcY— A term sometimes used instead of 
storage cell. 

CELL, SECONDARY OR STORAGE, CAPACITY OF— The 
product of the current in amperes, by the number of 
hours the battery is capable of furnishing said current, 
when fully charged, until exhausted. 

CELL, SELENTUjM — A cell consisting of a mass of selenium 
fused in between two conducting wires or electrodes of 
platinized silver or other suitable metal. 

CELL, ST07LAGE- A single one of the cells required to 
form a secondary battery. 

CELL, VOLTAIC- The combination of two metals, or of a 
metal and a metalloid, which, when dipped into a liquid 
or liquids called electrolj^tes, and connected outside the 
liquid or liquids by a conductor, will produce a current 
of electricity. 

CELL, VOLTAIC, BICHROMATE— A zinc-carbon couple 
used with an electrolj^te known as electropoion, a solu- 
tion of bichromate of potash and sulphuric acid in 
water. 



CEL 



298 



CELL, VCiLTATC, BUNSEN'S— A zinc-carbon couple, the 
elements of which are immersed respectively in electro- 
lytes of dilute siilphuric and strong" nitric acids. 

CELL, VOLTAIC, CLOSED-CIRCUIT— A voltaic cell that 
can be left for a considerable time on a closed circuit of 
comparatively small resistance without serious polari- 
zation. 



CELL, VOLTAIC, CONTACT THEORY OF— A theory which 
accounts for the production of difference of potential 
or electromotive force in the voltaic cell by the contact 
of the elements of the voltaic couple with one another 
by means of the electrolyte. 

CELL, VOLTAIC, DANIELL'S— A zinc-copper couple, the 
elements of which are immersed respectively in electro- 
lytes of dilute sulphuric acid, and a saturated solution 
of copper sulpliate. 

CELL, VOLTAIC, DOUBLE-FLUID—A voltaic cell in which 
two separate liuids or electrolj'tes are employed. 

CELL, VOLTAIC, DRY— A voltaic cell in which a moist ma- 
terial is used in place of the ordinary fluid electrolyte. 

CELL, VOLTAIC, FULLER'S MERCURY BICHROMATE— 
A zinc-carbon couple immersed in an electrolyte of elec- 
tropoion liquid. In whioh «the zinc is in contact with 
liquid mercury. 

CELL, VOLTAIC, GliAVITY— A zinc-copper couple, the ele- 
ments of which are employed with electrolytes of dilute 
sulphuric acid or dilute zinc sulphate, and a concentra- 
ted solution of copper sidphate respectively. 



299 GHA 

CELL, VOLTAIC, GKOVE— A zinc-platinum couple, the ele- 
mentfij of which are used with electrolytes of sulphuric 
and nitric acids respectively. 

CELL, VOLTAIC, LECLANCHE— A zinc-carbon couple, the 
elements of which are used in a solution of sal-ammo- 
niac and a finely divided layer of black oxide of man- 
g-anese respectively. 

CELL, VOLTAIC, OPEN-CIKCUIT— A voltaic cell that can 
not be kept on closed circuit, with a comparatively 
small resistance, for any considerable time without 
serious polarization. 

CELL, VOLTAIC, POLAEIZATION OF— The collection of a 
g-as, g-enerally hydrogen, on the surface of the negative 
element of a voltaic cell. 

CELL. VOLTAIC, SILVEK CHLOKIDE— A zinc and silver 
couple immersed in electrolytes of sal-ammoniac or 
common salt, in which chloride of silver is used as the 
depolarizer. 

CELL, VOLTAIC, SMEE— A zinc-silver couple used with an 
electrolyte of dilute sulphuric acid. 

CELL, VOLTAIC, STANDARD, CLARK'S— The form of 
standard cell designed by Latimer Clark, having an 
E. M. F. of 1.438 volts at 57 degrees F. 

CHARACTEKISTIC CURVE— (See Curve, Characteristic). 

CHARGE, DISSIPATION OF— The gradual but final loss of 
any charge by leakage, which occurs even in a well in- 
sulated conductor. 



CIR 



300 



CIIAPiGE, DTSTTaBUTION OF— The variations that exist 
in the density of an electrical charge at different por- 
tions of the surface of all insulated conductors except 
spheres. 

CHARGE, ELECTRIC— The quantity of electricity that ex- 
ists on the surface of an insulated electrified conductor. 

CHARGE, RESIDUAL— The charge possessed by a charged 
Lej'den jar for a few moments after it has been disrupt- 
:\e\y discharged by the connection of its opposite coat- 
ings. 

CHARGE, RETURN — A charge induced in neighboring con- 
ductors b.y a discharge of lightning. 

CHARGING ACCUIMULATORS— Sending an electric current 
into a storage battery for the purpose of rendering it 
an electric source. 



CHOKING COIL— (See Coil, Choking). 

CIRCUIT, CLOSED— A circuit is closed, completed, or made 
when its conducting continuity is such that the current 
can pass. 

CIRCUIT, CLOSED-MAGNETIC— A magnetic circuit which 
lies wholly in iron, or other substance of high magnetic 
permeability. 

CIRCUIT, CONSTANT-CURRENT— A circuit in which the 
current or number of amperes is maintained constant 
notwithstanding changes occurring in its resistance. 

CIRCUIT, CONSTANT POTENTIAL— A circuit, the poten- 
tial or number of volts of which is maintained approxi- 
mately constant. 



( 



301 CIR 

CIECUIT, EARTH— A circuit in which the ground or earth 
forms part of the conducting cath. 

CIRCUIT, ELECTIilC— The path in which electricity circu- 
lates or passes from a given point, a>ound or through a 
conducting path, back again to its starting point. 

CIRCUIT, EXTERIs\AL— That part of a circuit which is ex- 
ternal to, or outside the electric source. 

CIRCUIT, GROUND -A circuit in which the ground forms 
part of the path through which the current passes. 

CIRCUIT, INDUCTIVE— Any circuit in which induction 
takes place. 

CIRCUIT, INTERNAL— That part of a circuit which is in- 
cluded within the electric source. 

CIRCUIT, LOCAL-BATTERY— The circuit, in a telegraphic 
system, in which is placed a local battery as distin- 
guished from a main battery. 

CIRCUIT, MAGNETIC— The path through which the lines 
of magnetic force pass. 

CIRCUIT, NfETALLIC— A circuit in which the ground is not 
employed as any part of the path of the current, metal- 
lic conductors being employed throughout the entire 
circuit. 

CIRCUIT, MULTIPLE— A compound circuit, in which a 
number of separate sources or separate electro-receptiv^e 
devices, or both, have all their positive poles connected 
to a single positive lead or conductor, and all their neg- 
ative poleg to a single negative lead or conductor. 



CIR 



302 



CIKCUIT, MULTlPLE-SEiaES— A compound circuit in 
wliicli a number of separate sources, or separate elec- 
tro-receptive devices, or both, are connected in a num- 
ber of separate g-roups in series, and these separate 
g-roups subsequently connected in multiple. 

CIRCUIT, OPEN— A broken circuit. A circuit, the con- 
ducting- continuity of which is broken. 

CIllCUIT, KETUEN— That part of a circuit by which the 
electric current returns to the source. 

CIRCUIT, SERIES—A compound circuit in which the sep- 
arate sources, or the separate electro-receptive devices, 
or both, are so placed that the current produced in 
each, or passed throug-h each, passes successive! 3^ 
through the entire circuit from the first to the last. 

CIRCUIT, SERIES-MULTIPLE— A compound circuit, in 
which a number of separate sources, or separate elec- 
tro-receptive devices, or both, are connected in a num- 
ber of separate groups ih multiple-arc, and these sepa- 
rate groups subsequently connected in series. 

CIRCUIT, SHORT— A shunt, or by-path, of comparatively 
small resistance, around the poles of an electric source, 
or around any portion of a circuit, by which so much 
of the current passes through the new path, as virtually 
to cut out the part of the circuit around which it is 
placed, and so prevent it from receiving an appreciable 
current. 

CIRCUIT, SHUNT— A branch or additional circuit provided 
at any part of a circuit, through which the current 
branches or divides, part tlovving through the original 
circuit, and part through the new branch. 



303 COI 

CLARK'S STANDARD VOLTAIC CELL— (See CelL Voltaic, 
Standard, Clark's). 

CLEARANCE-SPACE— (See Space, Clearance). 

CLFATS, ELECTRIC— Suitably shaped pieces of wood, 
porcelain, hard rubber or other non-conducting material 
used for fastening* and supporting* electric conductors 
to ceilings, walls, etc. 

CLOCK, ELECTRIC— A clock, the works of which are mov- 
ed, controlled, regulated or wound, either entirely or 
partially, by the electric current. 

CLUTCH, CARBON, OF ARC LAMP— A clutch or clamp at- 
tached to the rod or other support of the carbon of an 
arc lamp, provided for gripping or holding the carbon. 

CODE, CIPHER — A code in which a number of words or 
phrases are represented by single words, or by arbitrary 
words or syllables. 

COIL, CHOKING — A coil of wire so wound on a core of iron 
as to possess high self-induction. 

COIL, IMPEDANCE— A term sometimes applied to a chok- 
ing-coil. 

COIL, INDUCTION — An apparatus consisting of two paral- 
lel coils of insulated wire employed for the production 
of currents by mutual induction. 

COIL, INDUCTION, MICROPHONE— An induction coil, in 
which the variations in the circuit of the primary are 
obtained by means of microphone contacts* (See Mi- 
crophone). 

COIL, KICKING — A term sometimes applied to a Choking- 
Coil. 



CO]M 



304 



UOJL, MAGNET — A coil of insulated wire surrounding the 
core of an electro-magnet, and through which the mag- 
netizing current is passed. 

COIL, PKTMATvY — That coil or conductor of an induction 
coil or transformer, through which the rapidly inter- 
rupted or alternate inducing currents are sent. 

COTL, EKSTSTAXCE— A coil of wire of known electrical 
resistance employed for measuring resistance. 

COTL, RESISTANCE, STANDARD— A coil the resistance of 
which is that of the standard ohm or some multiple or 
sub-multiple thereof. 

COTL, RUlIMKOIiFF — A term sometimes applied to any in- 
duction coil, the secondary of which gives currents of 
higher electromotive force than the primary. 

COIL, SECONDARY— That coil or conductor of an induc- 
tion coil or transformer, in which alternating currents 
are induced by the rapidly interrupted or alternating 
currents in the primary coil. 

COTL, SHUNT — A coil placed in a derived or shunt circuit. 

COIL, SPARK — A coil of insulated wire connected with the 
main circuit in a system of electric gas-lighting, the 
extra spark produced on breaking the circuit of v/hich 
is employed for electrically igniting gas jets. 

COILS, ARMATURE, OF DYNAMO-ELECTRIC MACHINE 
— The v.oils, strips or bars that are wound or placed on 
the armature core. 

COMMERCIAL EFFICIENCY— (See Efficiency, Commercial). 

C0:MMERCIAL efficiency of dynamo— (See Efficien- 
cy, Commercial, of Dynamo). 



305 COM 

COMMUTATION, DIAMETER OF— In a dynamo-electric 
machine a diameter on the commutator cylinder on one 
side of which the differences of potential, produced by 
the movement of the coils through the magnetic field, 
tend to produce a current in a direction opposite fo 
those on the other side. 

COMMUTATOE — In general, a device for changing the di- 
rection of an electric current. 

COMMUTATOE, DYNAMO-ELECTEIC MACHINE— That 
part of a dynamo- electric machine which is designed to 
cause the alternating currents produced in the arma- 
ture to flow in one and the same direction in the ex- 
ternal circuit. 

COMPASS, AZIMUTH— A compass used by mariners for 
measuriug the horizontal distance of the sun or stars 
from the magnetic meridian. A mariner's Compass. 

COMPASS, INCLINATION— A magnetic needle moving 
freely in a single vertical plane, and employed for deter- 
mining the angle of dip at any place. 

COMPONENT, HOEIZONTA'L,^OF EAETH'S MAGNETISM 
— That portion of the earth's directive force which acts 
in a horizontal direction. That portion of the earth's 
magnetic force which acts to produce motion in a com- 
pass needle free to move in a horizontal plane only. 

COMPOUND- WINDING OF DYNAMO-ELECTEIC MA- 
CHINES— (Sec \\^nding, Compound, of Dynamo-Elec- 
tric Machines). 

COMPOUND-WOUND DYNAMO-ELECTEIC MACHINE— 
(See Machine. Dynamo-Electric, Compound- Wound). 



J 






CON 3og 

'"'wou^^r^''^''^ MOTOK-(See Mote. Co^pouncl- 

COXDFXSER-A device for increasing the eapacitv oi an 

rd" frth" "'" "" "■'"^''^^ '' -- another in " 
ated earth-connected conductor, but separated there- 

TO take place through its mass. 

CONDENSER CAPACITY OF_The quantity of electricity 
.n cox, o^bs a condenser is capable of holdin.. beforli s 
potential ,n volts is raised a given amount 

''TncL:'^ ^'"^^ -"'''''''^ ^^-"^"'^ -"^-tin, sub- 

COXDUCTANCE-A word sometimes used in place of con- 
ducting- power. Conductivity. 

COXDUCTING POWER-(See PoM.r, Conducting). 

''''''SoZT' f ^^'^^^I'^^IC-A term sometimes em- 
aTeIectl:,;tr"^ ^'^ '''''''' °^ ^'^^^^^^^^ ^^-^-^ 

resistance. ^^'^^^^^-^he reciprocal of electric 

CONDUCa-OP-A substance which will permit the so-called 
passage of an electric current. A substance which nos 
sesses the ability of determining the direction twhS 
electricity shall pass through the ether or other de-ef 
•trjc surrounding- it. uie.ec 

"'"'^flL?''' "«"^-^™«-A term sometimes used for a 
iigntningf rod. 



307 CON 

CONDUCTORS, SERVICE— Conductors employed in sys- 
tems of incandescent lighting* connected to the street 
mains and to the electric apparatus placed in the sepa- 
rate building's or areas to be lighted. 

CONDUIT, TTNDEIiGKOUND ELECTRIC— An underground 
passageway or space for the reception of electric wires 
or cables. 

CONNECT — To place or bring into electric contact. 

CONNECTOR — A device for readily connecting or joining 
the ends of two or more wires. 

CONSEQUENT POLES— (See Poles, Consequent). 

CONSERVATION OF ENERGY— (See Energy, Conservation 
of). 

CONSTANT-CURRENT— (See Current, Constant). 

CONSTANT-CURRENT CIRCUIT— (See Circuit, Constant 
Current). 

CONSTANT POTENTIAL— (See Potential, Constant). 

CONST ANT-POITCNTIAL CIRCUIT— (See Circuit, Coji- 
stant-Potential) . 

CONTACT-BREAKER, AUTOMATIC— A device for causing 
an electric current to rapidly make and break its own 
circuit. 

CONTACT, METALIJC— A contact of a metallic conductor 
produced by its coming into firm connection with an- 
other metallic conductor. 



COK 308 

COIS'TACT, SLIDING— A contact connected with one part 
of a circnit that closes or completes an electric circuit 
by being- slid over a conductor connected with another 
part of the circuit. 

CONTROLLEK— A magnet, in the Thomson-Houston sys- 
tem of automatic regulation, whose coils are traversed 
by the main current, and bj^ means of which the regu- 
lator magnet is automatically thrown into or out of 
the main circuit on changes in the strength of the cur- 
rent passing. 

CONVECTIOiV, ELECTUOliYTIC— A term, proposed by 
Helmholtz to explain the apparent conduction of elec- 
tricity by an electrolj^te, without consequent decom- 
position. 

CONVEKTEPi— The inverted induction coil employed in 
systems of distribution by means of alternating cur- 
rents. A term sometimes used instead of transformer. 

CONVERTER, EFFICIENCY OF—The efficiency of a trans- 
former. 

CONVERTER, HEDGEHOG— A form of transformer. (See 
Transformer, Hedgehog). 

COrPER, STRAP— Copper conductors in the form of straps 
or fiat bars. 

CORD, ELECTRIC— A flexible, insulated electric conductor, 
generally containing at least two parallel wires. 

CORE ,ARMATrRE, H— An armature core the shape of the 
letter H, generally known as the shuttle armature, and 
sometimes as the girder armature. 



300 COU 

COKE, ARMATUKE, LAMTNATTON OF— The siibdi\dsion of 
the core of the armature of a dynamo-electrio machine 
into separate insn4ated plates or strips for the purpose 
of avoiding* eddy or Foucault currents. 

CORE. ARMATCTRE, OF DYNAMO-ELECTRTC MACHINE— 
The iron core, on, or around, which the armature coils 
of a dynamo-electric machine are wound or placed. 

CORE, ARMATURE, VENTILATION OF— Means for pass- 
ing* air through the armature cores of djmamo-electric 
machines in order to prevent undue accumulation of 
heat. 

CORE, LAMINATED— A core of iron which has been divid- 
ed or laminated, in order to avoid the injurious produc- 
tion of Foucalt or eddy currents. 

CORE, STRANDED, OF CABLE- The conducting wire or 
core of a cable formed of a number of separate conduc- 
tors or wires instead of a sing-le conductor of the same 
weig-ht per foot as the combined conductors. 

CORED CARP.ONS- (See Carbons, Cored). 

COULOMB — Such a quantity of electricity as would pass in 
one second in a circuit vt^hose resistance is one ohm, 
under an electromotive force of one volt. 

COUNTER- ELECTROMOTIVE FORCE— (See Force, Elec- 
tromotive, Counter). 

COUPLE, ASTATIC— Two magnets of exactly equal 
strength so placed one over the other in the same ver- 
tical plane as to completely neutralize each other. 



CUR 



no 



COUPLE, MAGNETIC— The ronple which tends to turn a 
mag-netic needle, placed in the earth's field, into the 
plane of the mag-netic meridian. • 

COUPLE, THERMO-ELECTPaC— Two dissimilar metals 
which, when connected at their ends only, so as 
to form a completed electric circuit, will produce a 
difference of potential, and hence an electric current, 
when one of the ends is heated more than the other. 

COUPLE, VOLTAIC— Two materials, usually two dissimilar 
metals, capable of acting as an electric source when 
dipped in an electrolyte, or capable of producing- a dif- 
ference of electric potential by mere contact. 

CROSS APtM— (See Arm, Cross). 

CROSS, ELECTRIC— A connection, generally metallic, acci- 
dentally established betw^een two conducting- lines. 

CRUCIBLE, ELECTRIC— A crucible in which the heat of 
the voltaic arc, or of electric incandescence, is employed 
either to perform difficult fusions, or for the purpose of 
effecting" the reduction of metals from their ores or the 
formation of alloys. 

CUP, POROUS— A porous cell. 

CURRENT, ALTERNATING— A current which flows aJter- 
nately in opposite directions. A current whose direc- 
tion is rapidly reversed. 

CURRENT, CONSTANT— A current that continues to flow 
for some time without varying* in strength. 

CURRENT, CONTINUOUS— An electric current which flows 
in one and the same direction. 



311 CUR 

CUI?RENT DENSITY-The current of electricity which 
passes in any part of a circuit as compared with the 
area of cross-section of that part of the circuit. 

CURRENT, DIRECT— A current constant in direction, as 
distinguished from an alternating current. 

CURRENT, DIRECTION OF— The direction an electric cur- 
rent is assumed to take out from one pole of any source 
through the circuit and its translating devices back to 
the source through its other pole. 

CURRENT. ELECTRIC— The quantity of electricity which 
passes per second through any conductor or circuit. 
The rate at which a definite quantity of electricity 
passes or flows through a conductor or circuit. 

CURRENT, ar':NE RATION OF, BY DYNAMO-ELECTRIC 
MACITTNF — The difFerence of potential developed in 
the armature coils by the cutting of the lines of mag- 
netic force of the field by the coils, during the rotation 
of the armature. 

CURRENT, INDUCED— The current produced in a conduc- 
tor by ci]tting lines of force. 

CURRENT, PULSATORY— A current, the strength of which 
changes suddenly. 

CURRENT, ROTATING— A term applied to the current 
which results by combining a number of alternating 
currents, whose phases are dis^jlaced with respect to 
one another. 

CURRENT STRENGTH— The product obtained by dividing 
the electromotive force by the resistance. 

The current strength for a constant current accord- 
ing to Ohm's law is — E 
C equals — 
R 



cim 



^i: 



CUREEXT, TO TRANSF0K:M A— To change the electromo- 
tive force of a current by its passage through a convert- 
er or transformer. To convert a current. 

CURRENT, UNIT STRENGTH OF— Such a strength of cur- 
rent that when passed through a circuit one centimetre 
in length, arranged in an arc one centimetre in radius, 
will exert a force of one dyne on a unit magnet pole 
placed at the center. This absolute unit is equal to ten 
amperes or practical units of current. 

CURRENTS, CO NAT^RTEP— Electric currents changed 
either in their electromotive force or in their strength, 
by passage through a converter or transformer. 

CURRENTS, EDDY— Useless currents produced in the pole 
pieces, armatures, field-magnet cores of dynamo-electric 
machines or motors, or other metallic masses, either bj'' 
their motion through magnetic fields, or by variations 
in tfhe strength of electric currents flowing near them. 

CURRENTS, EXTRA— Currents produced in a circuit by 
the induction of the current on itself on the opening 
or closing of the circuit. 

CURRENTS, FOUCAULT— A name sometimes applied to 
eddy currents, especially in armature cores. 

CURRENTS, HEATING EFFECTS OF— The heat produced 
by the passage cf an electric cuiTcnt through any cir- 
cuit. 

CURRENTS, SniPLE PERTOBIC— Currents, the flow ofi 
which is variable, both in strength and duration, ajid ir^ 
which the flow of electricity, passing any section of the 
conductor, may be represented by a simple periodic 
curve. 



313 CUT 

CURVE, CnAKACTERTSTIC— A diagram in which a curve 

is employed to represent the ratio of volts and am- 
pheres" in a dynam'o or motor. 

CUKYE, CHARACTEETSTIC, OF PARALLEL TRANSFOR- 
MER — A curve so drawn that its ordinate and abscissa 
at any point represent the secondary electromotive 
force and the secondary current of a multiple connected 
transformer, when the resistance of the secondary cir- 
cuit has a certain definite value. i 

CURVE, PERMEABILITy— A curve representing the mag- 
netic permeability of a magnetic substance. 

CURVE, SIMPLE-HARMONIC— The curve which results 
when a simple-harmonic motion in one line is com- 
pounded with a uniform motion in a straight line, at 
right angles thereto. 

A harmonic curve is sometimes called a curve of sines 
because the abscissas of the curve are proportional to 
the times, w^hile the ordinates are proportional to the 
sines of the angles, which ^re themselves proportional 
to the times. 

CUT-OUT, A — A device by means of whfch an electro-re- 
ceptive device or loop may be thrown out of the circuit 
of an electric source. 

CirT-OUT, AUTO:vrATIC, FOR MULTIPLE-CONNECTED 
ELECTRO-RECEPTICE DEVICES— A device for auto- 
matically cutting an electro-receptive device, such as a 
lamp, out of the circuit of the leads. 

Automatic cut-outs for incandescent lamps, when 
connected to the leads in multiple-arc, consist of stripa 
of readily melted metal called safety-fuses, which on 
the passage of an excessive current fuse, and thus auto- 
matically break the circuit in that particular branch. 



DKC 314 



CUTTING LINES OF .FOKCE-(See Force.Lines of Cutting.) 
CYCLE-A period of time within whicli a certain series of 
phenomena regularly recur, in the same order. 

CYCLE, MAONETIC-A single round of xna.netic change* 
to which a magnetizable substance, such as a piece^of 
iron, ,s subjected when it is magnetized from zero to a 
eertan. maximum magnetization, then decreased to 
zero, reversed and carried to a negative maximum, and 
then decreased again to zero. 



DAMPER-A metallic cylinder provided in an induction 
coil so as to partially or completely surround the iron 
core, for the purpose of varying the intensity of the 
currents induced in the secondary. 

DAMPING-The act of stopping vibratory motion such a, 
bringing a swinging magnetic needle quickly to rest 
so as to determine the amount of its deflection, without 
waiting until it comes to rest after repeated swin-in-.s 
to and fro. " '^ 



s 



DEAD-BEAT-Such a motion of a galvanometer needle in 
which the needle moves sharply over the scale from 
point to point and comes quickly to rest. 

DECLINATION-The variation of a magnetic needle from 
the true fireographieal north. 

DECLINATION, ANGLE OF-The angle which measure, 
the deviation of the magnetic needle to the east or west 
of the true geographical north. 



315 DIE 

DECOMPOSITION, ELKCTRIC— Chemical deeoiriposition by 
means of an electric discharge or current. 

DEMAGNETIZATION— A process, generally directly oppo- 
site to that for producing* a magnet, by means of which 
the magnet laay be deprived of its magnetism. 

DENSITY, MAGNETIC— The strength of magnetism as 
measured by the nnmber of lines of magnetic force 
that pass through a unit area of cross-section of the 
magnet, i. e., a section taken at right angles to the 
lines of force. 

DEPOSIT. ELECTRO-METALLrRGICAL— The deposit of 
metal obtained by an}^ electro- metallurgical process. 

DETECTOE, GROUND— In a system of incandescent lamp 
distribution, a device placed in the central station, for 
showing by the candle-power of a lamp the approxi- 
mate location of a srround on the svstem. 

DEVICE, ELECTRO-RECEPTIVE— Various devices placed 
in an electric circuit, and energized by the passage 
through them of the electric current. 

DEVICE, TRANSLATING— A term embracing electro-re- 
ceptive and magnefo-receptive devices. (See Device, 
Electro-Receptive). 

DIAMAGNETIC — The property possessed by substances 
like bismuth, phosphorus, antimony, zinc and numerous 
others, of being apparently repelled when placed be- 
tween the poles of powerful magnets. 

DIELECTRIC — A substance which permits induction to 
take place through its mass. 



DIS 316 

DTELECTRTC. POLAKTZATTOX OF— A molecular strain 
produced in the dielectric of a Leyden jar or other con- 
denser, by the attraction of the electric charg-es on its 
opposite faces, or by the electrostatic stress. 

DIMMER — A choking* coil or resistance employed for regu- 
lating the potential of the feeders, which usually carry 
incandescent lamps. 

DIP, MAGNETIC— The deviation of a magnetic needle from 
a true horizontal position. The inclination of the mag- 
netic needle towards the* earth. 

DIRECT CURRENT- (See Current, Direct). 

DIRECT-CURRENT ELECTRIC MOTOR— (See Motor, Elec- 
tric, Direct-Current). 

DIRECTION OF LINES OF FORCE— (See Force, Lines of, 
Direction of). 

DISC, ARx\GO'S — A disc of copper or other non-magnetic 
metallic substance, which, when rapidly rotated under 
a magnetic needle, supported independently of the disc, 
causes the needle to be deflected in the direction of 
rotation, and, when the velocity of the disc is sufficient- 

'■ ]y great, to rotate with it. 

DISC, FARADAY'S — A metallic disc movable in a magnetic 
field on an axis parallel to the direction of the field. 

DISCHARGE— The equalization of the difference of poten- 
tial between the terminals of a condenser or source, on 
their connection b}^ a conductor. 

DISCHARGE, BRUSH— A faintly luminous discharge that 
occurs from a pointed positive conductor. 



317 DIS 

DISCHARGE, DISEUPTIVE— A sudden, and more or less 
complete, discharge that takes place across an inter- 
vening* non-condnctor or dielectric. 

DISCHARGE, LUMINOUS EFFECTS OF— The luminous 
phenomena attending- and produced by an electric dis- 
charge. 

DISCHARGE, OSCILLATING— A number of successive dis- 
charges and recharges which occur on the disruptive 
discharge of a Leyden jar, or condenser. 

DISCHARGE, VELOCITY OF— The time required for the 
passage of a discharge through a given length of con- 
ductor. 

DISCHARGER, UNIVERSAL— An apparatus for sending 
the discharge of a powerful Leyden battery or condens- 
er in any desired direction. 

DISCONNECT— To break or open an electric circuit. 

DISTANCE, SPARKING— The distance at which electrical 
sparks will pass through an intervening air space. 

DISTILLATION, ELECTRIC— The distillation of a liquid in 
which the etTects of heat are aided b}^ an electrification 
of the liquid. 

DISTRIBUTION, CENTER OF— In a system of multiple- 
distribution, any place where branch cut-outs and 
switches are located in order to control communication 
therewith. The electrical center of a system of distri- 
Ivution ?.s regards the conducting network. 

DISTRIBUTION OF ELECTRICITY— (See Electrcity, Dis- 
tribution of). 



DYN 



318 



DISTRIBUTION OF ELECTRICITY BY CONSTANT PO- 
TENTIAL CI]iCI^IT— (See Electricity, Multiple Distri- 
bution of, by Constant Potential Circuit). 

DOUBLE-CARBON ARC LAMP— (See Lamp, Electric Arc, 
Double-Carbon ) . 

DOUBLE-FLinD VOLTAIC CELL— (See Cell, Voltaic, Dou- 
ble-Fluid). 

DOUBLE-TOUCH, MAGNETIZATION BY— A method for 
producing- mag-netization by the simultaneous touch of 
two magnet poles. 

DROP, ANN UNCI ATOR-^A movable signal operated by an 
electro-magnet, and placed on an annunciator, the drop- 
ping of Avhich indicates the closing or opening of the 
circuit with ^^hich the electro-magnet is connected. 

DROP, AUTOMATIC— A device for automatically closing 
the circuit of a bell and holding it closed until stopped 
b}^ resetting a drop. 

DRUM ARMATURE- (See Armature, Drum). 

DRY VOLTAIC CELL- (See Cell, Voltaic, Dry). 

DUPLEX TELEGRAPHY- (See Telegfaphy, Duplex). 

DYEING, PJLECTRIC— The application of electricity eithef 
to the reduction or the oxidation of the salts used in 
dyeing. 

DYNAMICS, ELECTRO— That branch of electric science 
which treats of the action of electric currents on one 
another and on themselves or on magnets. 

DYNAMO— The name frequently applied to a dynamo-elec- 
tric machine used as a generator. 



319 DYN 

DYNAMO, composite: FIELD— A dynamo whose field 
coils are series and separately excited. 

mNAMO, COMPOUND-WOUND— A compound-wound dy- 
namo-electric machine. (See Machine, Dynamo-Elec- 
tric, Compound-Wound). 

DYXAMO-ET.ECTTiTC MACHINE, BI-POLAE— (See Ma- 
chine, Jjynamo-Electric, Bi-Polar). 

DYNAMO-ELECTRIC MACHINE, MULTIPOLAE— (See Ma- 
chine, Dynamo-Electric, Multipolar). 

DYNAMO, INDUCTOPt- A dynamo-electric machine for al- 
ternating* currents in which the differences of potential 
causing- the currents are obtained by magnetic chang-es 
in the cores of the armature and field coils by the move- 
ment past them of laminated masses of iron inductors. 

DYNAMO, MULTIPHASE— A polyphase dynamo. (See Dy- 
namo, Polyphase. Dynamo, Rotating Current). 

DYNAMO, POLYPHASE— A dynamo producing two or 
more currents difi'ering in phase. A name sometimes 
applied to a rotating current dynamo. (See Dj^namo, 
Rotating Current). 

DYNAMO, PYROlSfAGNETIC— A name sometimes applied 
to a pyromagnetic generator. 

DYNAMO, SEPARATELY EXCITED— A separately-excited 
dynamo-electric machine. 

D7NAM0, SERIES — A series-wound dynamo-electric ma- 
chine. 

DYNAMO. SHUNT— A shunt-wound dynamo-electric ma- 
chine. 






<. 



EFF 



320 



DYNAMOjMEIT'K, ELECTRO— a form of g-alvanometer for 
the measurement of electric currents. 

DYNE — The unit of force. The force which in one second 
can impart a velocity of one centimetre per second to 
a mass of one gramme. 



E. — A contraction sometimes used for earth. A contraction 

sometimes used for electromotive force, or E. M. F., as 

in the well-known formula for Ohm's law, 

E 

C equals — 

R 

E. M. r. — A contraction generally used for electromotive 
force. 

p]AKT7I--A fault in a telegraphic or other line, caused by 
accidental contact of the line with the ground or earth, 
or with some conductor connected with the latter. 

EBONTTJC — A tough, hard, l)]ack substance, composed of 
india rubber and sulphur, which possesses high powers 
of insulation and of specific inductive capacity. 

EDDY CURRENTS— (See Currents, Eddy). 

EEL, ELECTRIC — An eel possessing the power of giving 
powerful electric shocks. The gymnotiis electricus. 

EFFECT, ED1S0N--An electric discharge which occurs be- 
tween one of the terminals of the incandescent filament 
of an electric lamp, and a metallic plate placed near 
the filament but disconnected therefrom, as soon as a 
certain difference of potential is reached between the 
lamp terminals. 



321 EFF 

EFFECT. FKriKANTI— An increase in the electromotive 
force, or difl'erence of potential, of mains or conductors 
towards the end of the same farthest from the termi- 
nals that are connected with a source of constant pi> 
tential. 

ICITECT, HALL — A transverse electromotive force, pro- 
duced by a magnetic field in substances underg*oin^ 
electric displacement. 

EFFECT, JOULE— The heating effect produced by the pass- 
age of an electric current through a conductor, arising 
merely from the resistance of the conductor. 

EFFECT, PELTIER— The heating effect produced by the 
passage of an electric current across a thermo-electric 
junction or surface of contact between two different 
metals. 

EFFECT, THEFtMO-ELECTRTC— The production of an elec- 
tromotive force at a thermo-electric junction by a dir- 
ference of temperature between that junction and the 
other junction of the thermo-electric couple. 

EFFECT, THOMSON— The production of an electromotive 
force in unequally heated homogeneous conducting sub- 
stances, k term also applied to the increase or decrease 
in the differences of temperature in an unequally heat- 
ed conductor, produced by the passage of an electrical 
current through the conductor. 

EFFECT, VOLTAIC— A difference of potential observed at 
the point of contact of two dissimilar metals. 



EFF 



322 



EFFICIENCY, COMMERCIAL— The useful or available cn- 
erg-y produoerl divided by the total energy absorbed by 
any njachine or apparatus. 
The Commercial Efficiency equals 

W W 

— equals 

M W-f-w-[-m, 

when W equals the useful or available energy; M equals 
the total energy; w, the energy absorbed by the ma- 
chine, and m, the stray power, or power lost in friction 
of bearings, etc., air friction, eddy currents, etc. 

EFFICIENCY, COMMERCIAL, OF DYNAMO— The useful 
or available electrical energy in the external circuit, 
divided by Ihe total mechanical energj^ required to drive 
the dynamo that produced it. 

EFFICIENCY, ELECTRIC— The useful or available electric- 
al energy of an^^ source, divided by the total electrical 
energy. 

W 

The electric efficiency equals , where W, equals 

W-j-w 

the useful or available electrical energy, and w, 
the electrical energy absorbed by the machine. 

EFFICIENCY OF CONVERSION— The ratio between the 
energy present in any result and the energy expended 
in producing that result. 

EFFICIENCY, QUANTITY, OF STORAGE BATTERY— The 
ratio of the n\imber of ampere-hours, taken out of a 
storage or secondary battery, to the number of ampere- 
hours put in the battery in charging it, 



323 ELE 

EFFICIEiVCY, REAL, OF STORAGE BATTERY— The ratio 
of the number of watt-hoiirs taken out of a storage 
battery, to the number of watt-hours put into the bat- 
tery in charging" it. 

ELECTRIC— Pertaining to electricity. 
ELECTRIC ARC— (See Arc, Electric). 
ELECTRIC BATTERY— (See flattery, Electric). 
ELECTRIC BOBBIX— (See Bobbin, Electric). 
ELECTRIC BUZZER~(See Buzzer, Electric). 
ELECTRIC CANDLE— (See Candle, Electric). 
ELECTRIC CHARGE— (See Charge, Electric). 
ELECTRIC CIRCUIT- (See Circuit, Electric). 
ELECTRIC CLOCK— (See Clock, Electric). 
ELECTRIC COIL— See Coil, Electric). 
ELECTRIC CURRENT— (See Current, Electrtc). 
ELECTRIC EFFICIENCY- (See Et!iciency, Electric). 
ELECTRIC ENERGY -(See Energy, Electric). 
ELECTRIC FiELD— (See Field, Electa Magnetic.) 
ELECTRIC FORCE— (See Force, Electric). 
ELECTRIC FURNACE— See Furnace, Electric). 
ELECTRIC FUSE— (See Fuse, Electric). 
ELECTRIC HEAT- (See Heat, Electric). 
ELECTRIC HORSE rO\FER-- (See FoWer, florse, Electric) 
ELECTRIC INSULATION— (See Insulation, Electric). 
ELECTRIC LAMP, ARC— (See Lamp, Electric, Arc). 



w 



ELE 324 

ELECTRIC LAMT', INCANDESCENT— (See Lamp, Electric, 
Incandescent). 

ELECTRIC LAUNCH— (See Launch, Electric). 

ELECTRIC LIGHT— (fsee Lig-ht, Electric). 

ELECTRIC LIGHTING, CENTRAL STATION-(See Sta- 
tion, Central). 

ELECTRIC LOCOMOTIVE— (See Locomotive, Electric). 
ELECTRIC METER— (See JVfeter, Electric). 
ELECTRIC MOTOR— (See ISIotor, Electric). 
ELECTRIC OSCILLATIONS— (See Oscillations, Electric). 
ELECTRIC POTENTIAL— (See Potential, Electric). 
ELECTRIC POWER— (See Power, Electric). 

ELECTRIC REwSISTANCE— (See Resistance, Electric). 
ELECTRIC RESONANCE— (See Resonance, Electric). 
ELECTRIC SHOCK -(See Shock, Electric). 
ELECTRIC TRAMWAY— (See Tramway, Electric). 

ELECTRIC WELDING— (See Welding-, Electric;. 

ELECTRIC WHIRL- (See Whirl, Electric). 

ELECTRIC WORK -(See Work, Electric). 

ELECTRICALLY— In an electrical manner. 

ELECTRICIAN — One versed in the principles and applica- 
tions ol: electrical scienctr. 

ELECTRICITY— The name given to the unknown thing, 
matter or tSDrce, or both, which is the cause of electric 
phenomena. 

Electricity, no matter how produced, is believed to 
be one and the same thine. 



^ 



325 ELB 

ELECTRICITY, ANIMAL—Electricity produced during life 
in the bodies of animals. 

All animals produce electricity during life. In some, 
such as the electric eel or torpedo, the amount is com- 
parativelj^ large. In others, it is small. 

ELECTRICITY, ATMOSPHERIC— The free electricity al- 
most always present in the atmosphere. 

ELECTRICITY, ATMOSPHERE, ORIGIN OF— The exact 
cause of the free electricity of the atmosphere is un- 
known. 

ELECTRIC IT^^ CONTACT— Electricity produced by the 
mere contact of dissimilar metals. 

ELECTRICITY, DISTRIBUTION OF— Various combina- 
tions of electric sources, circuits and electro-receptive 
devices wliereby electricity generated by the sources 
is carried or distributed to more or less distant electro- 
receptive devices by means of the various circuits con- 
nected therewith. 

ELECTRICITY, DISTRIBTITION OF, BY ALTERNATIN(5 
CURRENTS— A system of electric distribution by the 
use of alternating currents. 

ELECTRICITY, DISTRIBUTION OF, BY CONSTANT CUR- 
RENTS—A system for the distribution of electricity by 
means of direct, i. e., continuous, steady or non-alter- 
naiing currents, as distinguished from alternating cur- 
rents. 

ELECTRICITY, DOUBLE FLUID HYPOTHESIS OF— A 
hypothesis which endeavors to explain the causes of 
electric phenomena by the assumption of the existence 
of two different electric fluids. 



ELE 



326 



ELECTRICITY, FRICTIONAL— Electricity produced by 
friction. 

ELECTRICITY, GALVANIC— A term used by some in place 
of voltaic electricity. 

ELECTRICITY, HERTZ'S THEORY OF ELECTRO-MAC- 
NETIC RADIATIONS OR WAVES- A theory, noxv gen- 
erally accepted, ^vhich regards light as one of the ef- 
fects of electro-magnetic pulsations or waves. 

ELECTRICITY, MAGNETO— Electricity produced by the 
motion of magnets past conductors, or of conductors 
past niagnets. Electricity produced by magneto-elec- 
tric induction. 

ELECTRICITY, MULTIPLE-DISTRIBUTION OF, BY CON- 
STANT POl^ENTIAL CIRCUIT— Any system for the 
distribution of continuous currents of electricity in 
which the electro-receptive devices are connected to the 
leads in multiijle-arc or parallel. 

ELECTRICITY, NEGATIVE— One of the phases cf electri- 
cal excitement. The kind of electric charge produced 
on resin when rubbed with cotton. 

ELECTRICITY, POSITIVE— One of the phases of electric 
excitement. The kind of electric charge produced on 
cotton when rubbed against resin. 

ELECTRICITY, P\RO— Electricity developed in certain 
crystalline bodies bylmequallv' heating or cooling them 

ELECTRICITY, SERIES DISTRIBUTION OF, BY CON- 
STANT CURRENT CIRCUIT— Any system for the dis- 
tribution of constant currents of electricity in which 
the electro-receptive devices are connected to the line- 
wire or circuit in series. 



327 ELE 

ELECTEICTTY, SINGLE-FLUID HYPOTHESIS OF— A hy- 
pothesis which endeavors to explain the cause of elec- 
trical phenomena by the assumj^tion of the existence of 
a sing-le electric fluid. 

ELECTRICITY, STATIC— A term applied to electricity pro- 
duced by friction. 

ELECTRICITY, STORAGE OF— A term improperly employ- 
ed to indicate such a storage of energy as will enable it 
tc directl}^ reproduce electric energy. 

ELECTRICITY, THERMO— Electricity produced by differ- 
ences of temijerature at the junctions of dissimilar 
metals. 

ELECTRICITY, UNIT QUANTITY OF— The quantity of 
electricity conveyed bj' unit current per second. 

The practical unit quantity of electricity is the cou- 
lomb, v/hich is the quantity conveyed by a current of 
one ampere in one second. 

ELECTRICITY. VOLTAIC— Differences of potential pro- 
duced by the agency of a voltaic cell or battery. 

ELECTRIFICATION— The act of becoming electrified. The 
production of an electric charge. 

ELECTRIFY — To endow with electrical properties. 

ELECTROCUTION— Capital punishment by means of elec- 
tricity. 

ELECTRODE --Either of the terminals of an electric source. 

ELECTRODE, NEGATIVE— The electrode connected with 
the negative pole of an electric source. 

ELECTRODE, POSITIVE-The electrode coi^nected with 
the positive x^olc of an electric source. 



ELE 



328 



ELECTKODE, vSPONGE— A moistened sponge connected 
to one of the terminals of an electric source and acting 
as the electro -therapeutic electrode. 

ELECTRODES— The terminals of an electric source. 

ELECTRODES, CARLON, FOR ARC-LAMPS— Rods of arti- 
ficial carbon employed in arc lamps. 

These are more properly called simply arc-lamp car- 
bons. 

ELECTRODES, CORED— Carbon electrodes of a cylindrical 
shape provided with a central cylinder of softer carbon. 

ELECTROLIER— A chandelier for holding- electric lamps, 
as distinguished from a chandelier for holding gas- 
lights. 

ELECTROLYSIS— Chemical decomposition effected by 
means of an electric current. 

ELECTROLYTE, TOLARIZATION OF— The formation of 
molecular groups or chains, in which the poles of all 
the molecules of any chain are turned in the same 
direction, viz: with their positive poles facing the neg-i- 
tive plate, -^nd their negative poles facing the positive 
plate. 

ELECTROLYTIC OR ELECTROLYTICAL— Pertaining to 
electrolysis. 

ELECTROLYTIC CELL— (See Cell, Electrolytic). 

ELECTROLYTIC DECOMPOSITION— (See Decomposition, 
Electrolytic). 

ELECTRO-MAGNET— (See ISragnet. Electro). 

ELECTRO-METALLURGY— (See Metallurgy, Electro). 



329 ELE 

ELECTKOMETEK— An apparatus for measuring differ- 
ences of potential. 

ELECTEOMETEr:, CAPILLAKY— An electrometer in wliich 
a difference of potential is measured by the movemenr 
of a drop of sulphuric acid in a tube filled with mercury 

ELECIT.OMETEK, QITADRAT^T— An electrometer in which 
an electrostatic charge is measured by the attractive 
and repulsive force of four plates or quadrants, on a 
light needle of aluminum suspended within them. 

ELECTROMOTIVE FORCE— (See Force, Electromotive). 

ELECTROMOTIVE FORCE, BACK OR COUNTER— (See 
Force, Electromotive, Back). 

ELECTRO PHORUS— An apparatus for the production of 
electricity' by electrostatic induction. 

ELECTRO -PLATING— (See Plating, Electro). 

ELECTRO-PLATING BATH— (See Bath, Electro-Plating). 

ELECTROPOION LIQUID— (See Liquid, Electropoion). 

ELECTROSCOPE— An apparatus for showing the presence 
of an electric cliarge, or for determining its sign, 
whether positive or negative, but not for measuring its 
amount or value. 

ELECTROSCOPE, GOLD-LEAF— An electroscope in which 
two leaves of gold are used to detect the presence of 
an el<Bctric charge, or to determine its character wheth- 
er positive or negative. 

ELECTROSCOPE, PITH-BALL— An electroscope which 
shows the presence of a charge by the repulsion of two 
similarly charged pith-balls. 



^1 






EI/E 330 

ELECTROSTATIC CAPACITY— (See Capacity, Electro- 
static). 

ELECTROTONUS— A condition of altered functional activ- 
ity which occurs in a nerve when subjected to the action 
of an electric current. 

ELECTROTYI^E— A type, cast or impression of an object 
obtained by means of electro-metalhirg-y. (See Metal- 
lurg-y, Electro. Electrotyping) . 

ELECTROTYPIXG, OR THE ELECTROTYPE PROCESS— 
Obtaining casts or copies of objects by depositing met- 
als in molds by the agency of electric currents. 

The molds are made of wax, or other plastic sub- 
stance, rendered conducting by coating it with pon- 
dered plumbago. 

ELEMENT, N^EGATIVE, OF A VOLTAIC CELL— That ele- 
ment or plate of a voltaic cell into which the current 
passes from the exciting fluid of the cell. The plate 
that is not acted on by the electrolyte during the gen- 
eration of current by the cell. 

ELEMEXT, POSITIVE- That element or plate of a voltaic 
cell from which the current passes into the exciting 
fluid of the cell. The element of a voltaic couple which 
is acted on by the exciting fluid of the cell. 

ELEMENT, TIIER.\fO-ELECTRIC- One of the two metals 
or substances which form a thermo-electric couple. 

ELEMEXT, VOLTAIC— One of the two metals or sub- 
stances which form a voltaic couple. 

ELEVATOR, ELECTRIC- An elevator operated l^v electric 
power. 



331 ENE 

ELONGATrON, MAGNETIC— An increase in the length of 
a bar of iron on its magnetization. 

ENDOSMOSE, ELECTKIC— Differences in the level of li- 
quids capable of mixing through the pores of a dia- 
phragm separating them, produced by the flow of an 
electric current through the liquid. 

EiYERGY- -The power of doing work. 

ENERGY, CONSERVATION OF— The indestructibility of 
energ3^ 

The total quantity of energy in the universe is unal- 
terable. 

ENERGY, DISSIPx\TTON OF— The expenditure or loss of 
available energy. 

ENERGY, ET.ECTRIC— The power which electricity pos- 
sesses of doing work. 

ENERGY, ELECTRIC, TRANSMISSION OF— The transmis- 
sion of mechanical energy between two distant points 
connected by an electric conductor, by converting the 
mechanical energy into electrical energy at one point, 
sending the current so produced through the conduc- 
tor, and reconverting the electrical into mechanical en- 
ergy at the other point. 

ENERGY, KINETIC— Energy which is due to motion as 
distinguished from potential energy. 

ENERGY, POTENTIAL— Stored energy. Potency, or capa- 
bility of doing work. 

Energy possessing the power or potency of doing 
work, but not actually performing strch work. 

The capacity for doing work possessed by a body at 
rest, arising from its position as regards the earth, or 
from the position of its atoms as regards other atoms, 
with which it is capable of combining. 



EVA 33S 

ENERGY, RADIANT— Energy transferred to or charged on 
the universal ether. 

ENERGY, STAT1C--A term used fo express the energy 
possessed by a body at rest, resulting- from its position 
as regards other bodies in controdistinction to kinetic 
energy or the energy possessed by a body whose atoms, 
molecules or miisses are in actual motion. 
Potential energy. 

EQUATOR, MAGNETIC— The magnetic parallel or circle on 
the earth's surface where a magnetic needle, suspended 
so as to be J'l-ee to move in a vertical as well as a hori- 
zontal plane, remains horizontal. 

EQUIVALENT, ELECTRO-CHEAIICAL— A number repre- 
senting the v/eight in grammes of an elementary sub- 
stance liberated during electrolysis by the passage of 
one cou]omb of electricity. • 

EQUIVALENT, JOULE'S— The mechanical equivalent of 
heat. 

ERG — The unit o(f work, or the work done when unit force 
is overcome thrrriigh unit distance. The work accom- 
plished when a body is moved through a distance of 
one centimetre with the force of one dyne. 

ETIJER — The tenuo is, highly elastic iluid that is assumed 
vo fill all space, and hy vibrations or waves in which 
light and heat are transmitted. 

EVAPORATION, ELECTRIC— The formation of vapors at 
the surfaces of substances by the influence of negative 
electrification. 



533 FAR 

EVAPORATTON, KLECTEIFICATION BY— An increase in 
the difFerenee of potential existing, in a mi»ss of vapor 
attending its Sjudden condensation. 

EXCHANGE, TELEPHONIC, SYSTEM OF— A combination 
of circuits, switches and other devices, by means of 
which any one of a number of subscribers connected 
with a telephonic circuit, or a neighboring telephonic 
circuit or circuits, may be placed in electrical commun?- 
cntion with any other subscriber connected with such 
circuit or circuits. 

EXPLODEPt, ELECTPIC MINE— A small magneto-electric 
machine used to produce the currents of high electro- 
motive force eniployed in the direct tiring of blasts. 

EXPLODER, ELECTRO-MAGNETIC— (See Exploder, Elec- 
trie Mine). 

EXPLORER, MAGNETIC—A small, flat coil of insulated 
wire, used, in connection with the circuit of a tele- 
phone, f o determine the position and extent of the mag- 
netic leakage f»f a dynamo-electric machine ov other 
similar apparatus. 



FAHRENHEIT'S THERMOMETER SCALE— (See Scale, 
Thermometer, Fahrenheit's). 

FALL OF POTENTIAL— (See Potential, Fall of). 

FAN GUARD— (See Guard, Fan). 

FARAD — The practical unit of electric capacity. 

Such a capacity of a conductor or condenser that ona 
coulomb of electricity is required to produce in the con- 
ductor or condenser adiilerence of potential of one volt. 



FIB 



334 



FAKAD. MICRO— The millionth part of a farad. 

FAULT — Any failure in the proper working of a circuit 
due to ground contacts, cross-contacts or disconnec- 
tions. 

FEED, CLOCKWORK, FOR ARC LAMPS— An arrangement 
of clockwork for obtaining a uniform feed motion of 
one or both electrodes of an arc lamp. 

FEED, TO — To supply with an electric current, as by a 
dynamo or other source. 

FEEDER. — One of the conducting wires or channels 
through which the current is distributed to the main 
conductors, 

FEEDER, STAlSlDARD OR MAIN- -The main feeder to 
which the standard pressure indicator is connected, 
and whose pressure controls the pressure at the ends 
of all the other feeders. 

FEEDERS — In a system of distribution by constant poten- 
tial, as in incandescent electric lighting, the conducting 
wires extending between the bus-wires or bars, and the 
junction boxes. 

FEET, AMPERP] — The product of the current in amperes 
by the distance in feet through which that current 
passes. 

FIBRE, QUARTZ— A fibre suitable for suspending galvi- 
nometer needles, etc., made of quartz. 

FIBRE, VULCANIZED— A variety of insulating material 
suitable for liurposes not requiring the highest insu- 
lation. 



335 FIE 

FIELD, AIR — '.rhat portion of a iriagnetic field in which 
the lines of force pass through air only. 

FIELD, ALTERNATING— An electrostatic or magnetic 
field the positive direction cf the lines of force in which 
is alternately reversed or changed in direction. 

FIFLD, ALTERNATING MAGNETIC— A magnetic field the 
direction of whose lines of force is alternately reversed. 

FIELD, DENSITY GF— The number of lines of force that 
pass through any field, per unit of area of cross-sectio.i. 

FIELD, ELECTRO-MAGNETIC— The space traversed by the 
lines of magnetic force produced by an electro-magnet. 

FIEID, ELECTROSTATIC— The region of electrostatic in- 
fluence surrounding a charged body. 

FIELD, EXCITER OF— In a separately excited dynamo- 
electric machine, the dynamo-electric machine, voltaic 
battery, or otJier electric source employed to produce 
the field of the field magnets. 

FIELD, INTENSITY OF— The strength of a field as meas- 
ured by the niim.ber of lines of force that pass through 
it per unit of area of cross-section. 

FIEI-D, MAGNETIC- -The region of magnetic influence sur- 
rounding the i^oles of a magnet. 

A space or region traversed by lines of magnetic force. 

A place whei^ a magnetic needle, if free to move, will 
take up a definite position, under the influence of the 
lines of magnetic force. 

FIELD, MAGNETIC, OF AN ELECTRIC CURRENT— The 
magnetic field surrounding a circuit through which an 
electric current is flowing. 

An electric current produces a magnetic field. 



FIR 336 

FIELD, ^LVGNETIC, PULSATORY— A field, the strength of 
which pulsates in such manner as to produce- oscillatory 
currents by induction. 

FIELD, MAGNETIC, STRAY— That portion of the field of 
a dynamo-electric machine which is not utilized for the 
development of diiferences of potential in the armature, 
because its lines of force do not pass through the arm^.- 
ture. 

FIELD, MAGNETIC, STRENGTH OF— The dynamic force 
acting on a free magnetic pole, placed in a magnetic 
field. 

FIELD, ROTATING CURRENT— A magnetic field produced 
by means ox a rotating current. 

FIGURES, MAGNETIC— A name sometimes applied to the 
groupings of iron filings on a sheet of paper so held in 
a magnetic fi.eld as to be grouped or arranged under the 
influence of the lines of force of the same. 

FILAMENT OF INCANDESCENT ELECTRIC LAMP— (See 
Lamp, Incandescent Electric, Filament of). 

FIliAMENTS, FLASHED— Filaments f6r an incandescent 
lamp, that have been subjected to the flashing proce^js. 

FINDER, RANGE, ELECTRIC— A device by means of which 
the exact distance of an enemy's sHip or other target 
can be readily determined. 

FIRE ALARM, AUTOIMATIC— (See Alarm, Fire, Automat- 
ic). 

FIRE ALARM SIGNAL P>OX— (See Box, Fire Alarm Signal) 



337 FLU 

FIRE, HOT, ST. ELMO'S— A term proposed by Tesla for a 
form of powerful brush discharge between the second- 
ary terminals of a high frequency induction coil. 

FITTINGS OE FIXTURES, ELECTRIC LIGHT— The sock- 
ets, holders, arms, etc., required for holding or support- 
ing incandescent electric lamps, 

FIXTURES, TELEGRAPHIC— A term generally limited to 
the variously shaped supports provided for the attach- 
ment of telegraphic wires. 

FLASHED FILAMrjNTS~(See Filaments, Flashed). 

FLASHES, AURORAL— Sudden variations in the intensity 
of the auroral light. Intermittent flashes of auroral 
light that occur during the prevalence of an aurora. 

FLASHING OF DYNAMO-ELECTRIC MACHINE— (See Ma- 
chine, Dynamo-Electric, Flashing of). 

FLATS — A name sometimes applied to those parts of com- 
mutator segments the siirface of which, through wear, 
has become lower than the other portions. 

FLOW, MAGNETIC— The magnetic flux. 

FLOW OF CURRENT. ASSUMED DIRECTION OF— (See 
Current, Assumed Direction of Flow of). 

FLUID, DEPOLARIZING— An electrolytic fluid in a voltaic 
cell that prevents polarization. 

FLUORESCENCE— A property possessed by certaiu solid 
or liquid substances of becoming self -lunii nous while- 
exposed to light. 



FOK 



338 



FLUX, MAGNETIC—The number of lines of magnetic force 
that pass or flow throiig-h a magnetic circuit. The total 
number of lines of magnetic force in any magnetic field. 
The magnetic flux is also called the magnetic flow. 

FLYER, ELECTEIC— A wheel arranged so as to be set into 
rotation by the escape of convection streams from its 
points when connected with a charged conductor. 

FOCUS — A point in front or back of a lens or mirror, where 
all the rays of light meet or seem to meet. 

FOLLOWING HOIiX OF POLE PIECES OF DYNAMO- 
ELECTRIC MACHINE— (See Horns, Following of Pole 
Pieces of a Dynamo-Electric Machine). 

FOOT-POUND— A unit of work. 

FORCE — Any cause which changes or tends to change the 
condition of rest or motion of a body. 

FORCE, CENTRIFUGAL— The force that is supposed to 
urge a rotating body directly awaj' from the center of 
rotation. 

FORCE, COERCIVE— The power of resisting magnetization 
or demagnetization. 

FORCE, CONTACT -A difference of electrostatic potential, 
produced by tlie contact of dissimilar metals. 

FORCE, ELECTRIC— The force developed by electricity. 

FORCE, ELECTROMOTIVE— The force starting electricity 
in motion, or tending to start electricity in motion. 
The force which moves or tends to move electricity. 

FORCE, ELECTROMOTIVE, ABSOLUTE UNIT OF— A unit 
of electromotive force expressed in absolute or C. G. S. 
anitp. The one-hundred millionth part of a volt, since 
1 volt equals 108 C. G. S. units of electromotive force. 



339 FOR 

FOKCE, ELECTEOMOTIVE. AYEIiAGE OR MEAN— The 
sum of the \alues of a number of separate electromo- 
tive forces divided by their number. 

FORCE, ELECTROMOTIVE, BACK— A term sometimes 
used for counter electromotive force. 

Counter electromotive force is the preferable term. 

FORCE, ELECTROMOTIVE COUNTER— An opposed or re- 
verse electromotive force, which tends to cause a cur- 
rent in the opposite direction to that actually produced 
by the source. In an electric motor,, an electromotive 
force contrary to that produced by the current which 
drives the motor, and which is proportional to the ve- 
locity attained by the motor. 

FORCE, ELECTROMOTIVE, DIRECT— An electromotive 
force acting- in the same direction as another electro- 
motive force already existing*. 

FORCE, ETiECTROMOTIVE, EFFECTIVE— The difference 
between the direct and the counter electromotive force. 

FORCE, ELECTROMOTIVE, IMPRESSED— The electromo- 
tive force acting on any circuit to produce a current 
therein. 

FORCE, ELECTROMOTIVE. INVERSE— An electromotive 
force which acts in the opposite direction to auother 
electromotive force already existing. 

FORCE, ELECTROMO^ITVE, OF INDUCTION— The electro- 
motive force developed by any inductive action. 

In a coil of wire undergoing induction, the value of 
the induced electromotive force does not depend in any 
manner on the nature of the material of which the coil 
is composed. 



FOll 340 

FORCE, ELECTROMOTIVE, OF SECONDARY OR STOR- 
AGE CELL, TIME-FALL OF— A gradual decrease ia the 
potential dilference of a storage battery observed dur- 
ing the discharge of the same. 

FORCE, ELECTROMOTIVE, OF SECONDARY OR STOR- 
AGE CELL, TIME-RISE OF— A gradual increase in the 
potential diifcrence of a secondary or storage cell ob- 
served on beginning the discharge after a prolonged 
rest. 

FORCE, ELECTR0:\I0TIVE, SECONDARY IMPRESSED— 
An electromotive force produced which varies in such 
manner as to produce a simple periodic current, or an 
electromotive force the variations of which can be cor- 
rectly represented by a simple-periodic curve. 

FORCE, ELECTROMOTIVE THERMO— An electromotive 
force, or ditference of potential, produced by differences 
cf temperature acting at thermo-electric junctions. 

FORCE, ELECTROMOTIVE VIRTUAL, OR EFFECTIVE— 
The square root of the mean siquare of an alternating 
or variable current. 

FORCE, EIECTl^OSTATIC- The force producing the at- 
tractions or repulsions of charged bodies. 

FORCE, ELECTROSTATIC, LINES OF— Lines of force pro- 
duced in the neighborhood of a charged body by the 
presence of the charge. 

Lines extending in the direction in which the force 
of electrostatic attraction or repulsion acts. 

FORCE, LINES OF, CUTTING— Passing a conductor 
through lines of magnetic force, so as to cut to inter- 
sect them. 



341 FOR 

FORCE LINES OF, DIRECTION OF— It is generally 
agreed to consider the force lines of magnetic force 
as coming out of the north pole of a magnet and pass 
ing into its south pole. 

FORCE, LOOPS OF~A term sometimes employed in the 
sense of lines of force. 

FORCE, MAGNETIC— The force which causes the attrac- 
tions cr repulsions of magnetic poles. 

FORCE, MAGNETIC, LINES OF— Lines extending in the 
direction in which the magnetic force acts. 

Lines extending in the direction in which the force of 
magnetic attraction or repulsion acts. 

FORCE, MAGNETIC, LINES OF, CONDUCTING POWER 
FOR — A term employed by Faraday for maignetic per- 
meability. 

FORCE, MAGNETO-MOTIVE— The force that moves or 
drives the lines of magnetic force through a magnetic 
circuit against the magnetic resistance. 

FORCE, MAGNETO-MOTIVE, PRACTICAL UNIT OF— A 
value of the magneto-motive force equal to 4// multi- 
plied by the amperes of one turn, or to 1-10 of the abso- 
lute unit, 

FORCE, TUBES OF— Tubes bounded by lines of electro- 
static or magnetic force. 

FORCE, TWISTING— A term sometimes used for torque. 

FORCE, UNIT OF— A force which, acting for one second 
on a mass of one gramme, will give it a velocity of one 
centimetre per second. 

Such a force of unit is called a dyne. 



FRO 342 

FORCES, PARALLELOGRAM OF—A parallelogram con- 
structed about the two lines that represent the direc- 
tion and intensity/ ^vith which two forces are sim-ulta- 
neously acting on a body, in order to determine the 
direction and intensity of the resultant force with 
which it moves. 

FORK, TROLLP:!^— The mechanism which mechanically 
connects the trolley wheel to the trollej^ pole. 

FORMIXG PLATES OF SECONDARY OR STORAGE 
CELLS — (See Plates of Secondary or Storage Cells, 
Forming of). 

FORMULAE — Mathematical expressions for some general 
rule, law or in^nciple. 

FOUCAULT CURRENTS— (See Currents, Foucault). 

FREE MAGNETIC POLE~(See Pole, Magnetic, Free). 

FREQUENCY OF ALTERNATIONS— (See Alternations, 

Frequency of). 
FRICTIONAL ELECTRICAL MACHINE— (See Machine, 

Frictional Electric). 

FRICTIONAL ELECTRICITY— (See Electricity, Frictional) 

FROG, GALVANOSCOPIC— The hind legs of a recently 
killed frog employed as an electroscope or galvanoscope 
by sending an electric current from the nerves to the 
muscles. 

FROG, TROLLEY— The name given to the device employed 
in fastening or holding together the trolley wires at 
any point where the trolley wire branches, and prop- 
erly guiding the trolley wheel along the trolley wire on 
the movement of the car over the track. 



343 GAL 

FURNACE, ELECTRIC— A furnace in which heat gener- 
ated electrically^ is employed for the purpose of effect- 
ing* difficult fusions for the extraction of metals from 
their ores, or for other metallurg-ical operations. 

FUSE BLOCK— (See Block, Fuse). 

FUSE BOX— (See Box, Fuse). 

FUSE, BRANCH— A safety fuse or strip placed in a branch 
circuit. 

FUSE, CONVERTER— A safety fuse connected with the 
circuit of a converter or transformer. 

FUSE, ELECTRIC— A device for electrically igniting a 
charge of powder. 

FUSE, MAIN — A safety fuse or strip placed in a main cir- 
cuit. 

FUSE, SAFETY— A strip, plate or bar of lead, or some 
readily fusible alloy, that automatically breaks the cir- 
cuit in whw'ch it is placed on the passage of a current 
of sufficient power to fuse such strip, plate or bar, when 
such current would endanger the safety of other parts 
of the circuit. 



GAINS — The spaces cut in the faces of telegraph poles for 
the support or placing of the cross arms. 

GALVANIC BATTERY— (See Battery, Galvanic). 

GAI-VANIC CELT.— (See Cell, Voltaic). 

GALVANIC POLARIZATION— (See Polarization, Galvanic). 



GAL 



344 



GALVANIC TASTE— (See Taste, Galvanic). 

GALVANISM — A term sometimes employed to express the 
effects produced by voUaic electricity. 

GALVANIZATION, ELECTr.O-METALLURGICAL — The 
process of covering- any conductive surface with a me- 
tallic coating' hy electrolytic deposition, such, for ex- 
ample, a? the thin copper coating* deposited on the car- 
bon pencils or electrodes used in systems of arc light- 



GALVANOMETER — An apparatus for measuring* the 
streng-th of an electric current by the deflection of a 
magnetic needle. 

The g-alvanometer depends for its operation on the 
fact that a conductor, throug-h which an electric cur- 
rent is flowing*, will deflect a magnetic needle placed 
near it. This deflection is due to the magnetic field 
caused by the current. 

GALVANOMETER, ABSOLUTE— A galvanometer whose 
constant can be calculated with an absolute calibration. 

GALVANOMETER, ASTATIC— A galvanometer, the needle 
of which is astatic. 

GALVANOMETER, BALLISTIC— A galvanometer designed 
to measure the strength of currents that last but a mo- 
ment, such, for example, a& the current caused by the 
discharge of a condenser. 

GALVANOMETER CONSTANT— (See Constant, Galvanom- 
eter). 

GALVANOMETER, T3EAB-BEAT — A galvanometer, the 
needle of which comes quickly to rest, instead of swing- 
ing repeatedly to-and-fro. (See Damping). 



345 GAL 

GALYANOMETETl, DEPREZ-D'ARSONVAL— A form of 
dead-beat galvanometer. 

GALVAA^0:METER, differential— a galvanometer con- 
taining' two coils so wound as to tend to deflect the nee- 
dle in opposite directions. 

GALVAN0:METER, figure of merit of— The recipro- 
cal of the current required to produce a deflection of 
the galvanometer needle through one degree of the 
scale. I 

GALVANOMETER, MARINE- A galvanometer devised l>y 
Sir William Thomson for use on steamships where the 
motion of magnetized masses of iron would seriously 
disturb the needles of ordinary instruments. 

GALVANOMETER, MIRROR— A galvanometer in which, 
instead of reading the deflections of the needle directly 
by its movements over a graduated circle, they are read 
by the movements of a spot of light reflected from a 
mirror attached to the needle, 

GALVANOMETER, REFLECTING— A term sometimes ap- 
plied to a mirror galvanometer. 

GALVANOMETER, SENSIBILITY OF— The readiness and 
extent to which the needle of a galvanometer responds 
to the jjassage of an electric current through its coils. 

GALVANOMETER, SINE— A galvanometer in which a ver- 
tical coil is movable around a vertical axis, so that it 
can be made to follow the magnetic needle in its deflec- 
tions. • 

In the sine galvanometer, the coil is moved so as to 
follow the needle until it is parallel with the coil. Un- 
der these circumstances, the strength of the deflecting 
currents in any two different cases is proportional to 
the sines of the anples of deflection. 



GAS 346 

GALVANO.ArETErt, TANGENT— An instrument in wliich 
the deflecting coil consists of a coil of wire within 
which is placed a needle very short in proportion to 
the diameter of the coil, and supported at the center 
of the coil. 

The galvanometer acts as a tangent galvanometer 
only when the needle is Yery small as compared with 
the diameter of the coil. The length of the needle 
should be less than one-twelfth the diameter of the coil. 

GALV\NO]\rETEri, TORSION— A galvanometer in which 
the strength of the deflecting current Is measured by 
the torsion exerted on the suspension system. 

GAP, AIH — A gap, or opening in a magnetic circuit con- 
taining air only. 

GA.P, ATR, MAGNETIC— A gap filled with air which exists 
in the opening at any part of a core cf iron or other 
m.edium of high permeability. 

GAP, SPAEK — A gap forming part of a circuit between 
two opposing conductors, separated by air, or other 
similar dielectric which is closed by the formation of a 
spark only when a certain difference of potential is 
attained. 

GAS, DTELECTKIC, STRENGTH OF— The strain a gas is 
capable of bearing without suffering disruption, or 
without permitting a disruptive discharge to pass 
1h rough it. 

GAS-LIGHTING, MULTIPLE ELECTRIC— A system of 
electric gas-lighting in which a number of gas-jets are 
lighted by means of a discharge of high electromotive 
force, derived from a Ruhmkorff coil or a static induc- 
tion machine. 



347 GEN 

GASSING— The evolution of gas from the plates of a stor- 
age or secondary cell. 

GAUGE, BATTERY— A form of portable galvanometer, 
suitable for ordinary test work. 

GAUGE, WIRE, AMEPtTCAN— A name sometimes applierl 
to the Erowm & Sharpe Wire Gauge. 

GAUGE, WIRE, BIRMINGHAM— A term sometimes applied 
to one of the English wire gauges. 

GAUGE, WIRE. MICROMETER— A gauge employed for ac- 
curately measuring the diameter of a wire in thou- 
sandths of an inch, based on the principle of the vernier 
or micrometer. 

GAUSS— The unit of intensity of magnetic field. 

GAUSS, FLEMING'S- Such a strength of magnetic field as 
is able to develop an electromotive force of one vot in 
a wire one million centimetres in length moved through 
the field with unit velocity. 

GAUSS, S. P. THOMPSON'S- Such a strength of magnetic 
field that its intensity is equal to 108 C. G. S. units. 

GAUSS, SIR WILLIAM THOMSON'S— Such an intensily of 
magnetic field as would be produced by a current of <me 
ampere at the distance of one centimetre. 

GENERAl'OR, DYNAMO-ELECTRIC— An apparatus in 
which electricity is produced by the mechanical move- 
ment of conductors through a magnetic field so as to 
cut the lines of force. A dynamo-electric machine. 

GENERATOR, MOTOR— A dynamo-electric generator in 
which the power required to drive the dj^namo is ob- 
tained from an electric current. 



GRA 348 

GEXERATOK, PYRO-MAGXETIC— An apparatus for pro- 
ducing" electricity directly from heat derived from the 
burning" of fuel. 

GERMAX SILVER ALLOY- (See Alloy, German Silver). 

GIMRA.LS^- Concentric rings of brass, suspended on pivots 
in a compass box, and on which the compass card Is 
supported so as to enable it to remain horizontal not- 
\\ithstanding the movements of the ship. 

GLOBE, VAPOR, OF IXCAXDESCEXT LAMP— A glass 
globe surrounding the chamber of an incandescent elec- 
tric lamD, for the purpose of enabling the lamp to be 
safely used in an explosive atmosphere, or to permit 
the lamp to be exposed in places where water is liable 
to fall on it. 



GOVERXOR, CURREXT— A current regulator. A device 
for maintaining constant the current strength in any 
circuit. 

GOVERXOR, ELECTRIC--A device for electrically controll- 
ing the speed of a steam engine, the direction of cur- 
rent in a plating bath, the speed of an electric motor, 
the resistance of an electric circuit, the flow of water 
or gas into or from a containing vessel, or for other 
similar purposes. 

GRAME— A unit of weight equal to 15.43235 grains. 

The grame is equal to the weight of one cubic cen- 
tin«( tre of pure watt^r ai the teinperaruro of its maxi- 
mum density. 

GRA^fOPHOXE -An apparatus for recording and repro- 
ducing articulate speech. 



349 GUT 

(jRAPHlTE— A soft variety of carbou suitable for writing 
on paper or similar surfaces. 

OKAY'S HAK^IONTC TELEGRAPHY— (See Telegraphy, 
Gray's Harmonic Multiple). 

GRAVITATION— A name applied to ihe force which causes 
masses of matter to tend to move towards one another. 

GRAVITY, CENTRE OF— The centre of weight of a body. 

GRID — A lead plate, provided with perforations, or other 
irregularities of surface, and employed in storage cells 
for the support of the active material. The support 
provided for the active material on the plate of a sec- 
ondary or storage cell. 

GROTHUSS' HYPOTHESIS— (See Hypothesis, Grothuss). 

GROUND DETECTOR— (See Detector, Ground). 

GROUND OR EARTH— A general term for the earth when 

employed as a conductor, or as a large reservoir of 

electricity. 

GROUND-RETURN— A general term used to indicate the 
use of the ground or earth for a part of an electric 
circuit. The earth or ground which forms part of the 
return path of an electric circuit. 

GROUND-WIRE — The wire or conductor leading to or con- 
necting with the ground or earth in a grounded circuit. 

GUARD, FAN — A wire netting placed around the fan of an 
electric motor for the purpose of preventing its revolv- 
ing arms from striking external objects. 

GUTTA-PERCHA —A resinous gum obtained from a tropi- 
cal tree and valuable electrically for its high insulating 
powers. 



HAR 350 

GYMNOTUS ELECTRIC US— The electric eel. 

H 

H. — A contraction for the horizontal intensity of the earth's 
maTOetism. 

II. — A contraction used in mathematical writing's for the 
magnetizing- force that exists at any point, or, g-ener- 
ally, for the intensity of the magnetic force. 

The letter H, when nsprl in mathematical writings or 
formulae for the intensity of the magnetic force, is 
always represented in bold or heavy faced type, thus: H 

HAIR, ELECTROLYTIC REMOVAL OF— The permanent 
removal of hair from any part of the body, by the elec- 
trolytic destruction of the hair follicles. 

HALF-SHADES FOR INCANDESCENT LAMPS— Shades 
for incandescent electric lamps, in which one-half of 
the lamp chamber proper is covered with a coating of 
silver, or other reflecting- surface for reflecting the 
light, or is ground for the purpose of diffusing the lig-ht. 

HANDIIOLE OF CONDUIT— A box or opening communi- 
cating- with an underground cable, provided for readily 
tapping- the cable, and, of sufficient size to permit of the 
introduction of the hand. 

HANGER, DOUBLE-CURVE TROLLEY— A trolley hanger 
g-enerally employed at the ends of single and double 
curves, and on intermediate points on double tra(»k 
curves, supported by lateral strain in opposite direc- 
tions. 

HATsTiER, TROLLEY— A device for supporting and prop- 
erly insulating trolley wires. 

HARMONIC RECEIVER— (See Receiver, Harmonic). 



351 HEA 

HARMONIC TELEGEAPH— (See Telegraphy, Gray's Har- 
monic Multiple). 
HEAD LIGHT, LOCOMOTIVE, ELECTEIC— An electric 
lig-lit placed in the focus of a parbolic reflector in front 
of a locomotive engine. 

The lamp is so placed that its voltaic arc is a little 
out oi the focus of the reflector, so that, by giving a 
slight divergence to the reflected light, the illumination 
extends a short distance on either side, of the tracks. 
HEAT — A form of energy. 

The phenomena of heat are due to a vibratory motion 
impressed on the molecules. Heat is transmitted 
through space by means of a wave motion in the univer- 
sal ether. This wave motion is the same as that caus- 
ing light. 

A hot body loses its heat by producing a wave lao- 
tion in the surrounding ether. This process is called 
radiation. (See Eadiation). 

The energy given off by a heated body cooling is 
called radiant energy. 
HEAT ELECTEIC— Heat produced by means of electric 

current. 
HEAT, MECHANICAL EQUIVALENT OF— The amount of 
mechanical energy, converted into heat, that would be 
required to raise the temperature of 1 pound of water 1 
degree Fahr. 

The mechanical equivalence between the amount of 
energy expended and the amount of heat produced, as 
measured in heat units. 

Rowland's experiments, the results of which are gen- 
erally accepted, gave 778 foot-pounds as the energy 
equivalent to that expended in raising the temperature 
of 1 pound of water from 39 degrees F. to 40 degrees F. 



TTEN 



353 



HEAT, SPECIFIC—The capacity of a substance for heat as 
compared with the capacity of an equal quantity of 
some other substance taken as unity. 

Water is sfenerall^^ taken as the standard for compari- 
son, because its capacity for heat is greater than that 
of any other common substance. 

HEAT UNIT— The quantity of heat required to raise a 
given weight of water through a single degree, 

(1.) The British 'Heat Unit, or Thermal Unit, or 
the amount of heat required to raise 1 pound of w^ater 
at greatest density 1 degree Fahr. This unit represents 
an amount of work equal to 778 foot-pounds. 

(2.) The Greater Calorie, or the amount of heat re- 
quired to raise the temperature of 1,000 grames of 
water 1 degree C, ^See Calorie). 

(3.) The Smaller Calorie, or the amount of heat re- 
quired to raise the temperature 1 gramme of water 1 
degree C. 

(4.) The Joule, or the quantity of heat developed in 
one second by the passage of a current of one ampere 
through a resistance of one ohm. 

HEATEE.ELECTRTC— A device for the conversion of elec- 
tricity into heat for piirposes of artificial heating. 

HEDGEHOG TrvANSFOKMER— (See Transformer, Hedge- 
Log). 

HENTIY, A- -The practical unit of self-induction. 

A circuit has a self-induction of one Henry when a 
change of one ampere per second produces in it a coun- 
ter E. M. F. of one volt. 



L 



35^ HOB 

HIGH-BARS — A term applied to those commutator seg*- 
ments, or paits of commutator segments, which, 
through less wear, faulty coustruction or looseness, are 
higher than adjoining portions. 

HOLDERS, CARBON, FOR ARC LAMPS— A clutch or clamp 
attached to the end of the lamp rod or other support, 
and provided to hold the carbon pencils used on arc 
lamps. 

HOLDERS FOR BRUSHES OF DYNAMO-ELECTRIC MA- 
CHINE — A device for holding the collecting brushes of 
a dynamo-electric machine. 

HOLTZ MxVCHINE-(See Machine, Holtz). 

HOOD FOR ELECTRIC LAMP— A hood provided for the 
double purpose of protecting the body of an electric 
lamp from rain or sun, and for throwing Its light in a 
general downward direction. 

HORIZONTAL COMPONENT OF EARTH'S MAGNETISM— 
(See Component, Horizontal, of Earth's Magnetism). 

HORNS, FOLLOWING, OF POLE PIECES OF A DYNAMO- 
ELECTRIC MACHINE— The edges or terminals of the 
pole pieces of a dynamo-electrical machine from which 
the armature is carried during its rotation. 

HORNS, LEADING, OF POLE PIECES OF A DYNAMO- 
ELECTRIC MACHINE— The edges or terminals of the 
pole pieces of a dynamo-electrical machine from which 
the armature is carried during its rotation. 

HORSE-POWER— A commercial unit for power or rate of 
doing work. 

HORSE-POWER, ELECTRIC- (See Power, Horse, Electric). 



HYS 



354 



HOESESTTOE MAGNET— (See Magnet, Horseshoe). 
HOTEL ANNUNCIATOFv— (See Annunciator, Hotel). 

HOUR, A]\[PEPtE— A unit of electrical quantity equal to 
one ampere flowing- for one hour. 

HOUR, HOPwSE-POWER— A unit of work. 

An amount of work equal to one-horse power for an 
hour. 

One horse power is equal to 1,980,000 foot-pounds, or 
745.941 w^att hours. 

HOUR, KILO-WATT— A unit of electrical power equal to 
a kilo-watt maintained for one hour. -' -^' 

HOUR, LAMP — Such a service of electric current as will 
maintain one electric lamp during* one hour. 

HOUR, WATT— A unit of electrical work. 

An expenditure of electrical work of one watt for 
one hour. 

HUMAN PODY, ET-ECTRICAL RESISTANCE OF— (See 
Body, Human, Resistance of). 

HYDROGEN, ELECTROLYTIC— Hydrogen produced by 
electrolytic decomposition. 

HYPOTHESIS, GROTHUSS— A hypothesis produced by 
Grothuss to account for the electrolytic phenomena 
that occur on closing the circuit of a voltaic cell. 

H^^STERESIS— Molecular friction to magnetic change of 
stress. 

A retardation of the magnetizing or demagnetizing 
effects as regards the causes which produce them. 

The quality of a jjaramagnetic substance by virtue of 
which energy is dissipated on the reversal of its mag- 
netization. 



355 INC 

I 

I. H. P. — A contraction for indicated horse-power, or the 
horse-power of an engine as obtained by the means of 
an indicator card. 

IGNITION, ELECTRIC— The ignition of a combustible ma- 
terial by heat of an electric origin. 

ILLUMINATION, ARTIFICIAL— The employment of artifi- 
cial sources of light. 

ILLUMINATION, UNIT OF— A standard of illumination 
prc^ os'^d by Preece, equal to the illumination given by 
a standard candle at the distance of 12.7 inches. 

IMPEDANCE- Generally any opposition to current ilow. 
A quantity which is related to the strength of the 
impressed electromotive force of a simple periodic or 
alternating current, in the same manner that resistance 
is related to the steady electromotive force of a con* 
tinuous current. 

IMPEDANCE COIL— (See Coil, Imipedance). 

IMPRESSED F;:.ECTR0M0TIVB FORCE— (See Force, Elec- 
troonotive, Impressed), 

INCANDESCE — To shine or glow by means of heat. 

INCANDESCENCE, ELBCTRlC^The shining or glowing of 
a substamce, generally a solid, by means of heat of elec- 
tric origin. 

INCLINATION, ANGLE OF— The angle which a magnetic 
needle, free to move ini a horizontal plane, miakes witu 
a horizontal line passing through its»point of support. 
The angle of magnetic dip. 



IXD 



356 



IN^CANDESCENT ELECTRIC T^MP— (See Lamp, Electric, 
Incandescent). 

INCLINATION, MAG.NBTIC— The angular deviation from 
a horizontal position of a freely suspended magnetic 
needle. 

INDIA RUBBER — A resinous substa.nice obtained froon the 
milky juice of several tropical trees. 

INDICATOR, ELECTRIC— ^A name applied to various de- 
vices, generally operated 'by the deflection ol a mag- 
r.etic needle, or the ringing of a bell, or both, for indi- 
caiting, at some distant point, the condition of an elec- 
tric circuit, the 'strength of current that is passing 
through it, the height of water or other liquid, the 
p»ressure 0>ni a boiler, the tetmperature, the* speed of an 
engine or line of shafting, the working of a machine or 
other similar events or occurrences. 

INDICATOR, ELECTRIC, FOR STEAMSHIPS— An electric 
indicator operated by circuits connected with the throt- 
tle valve and reversing gear of the steam engine. 

INDICATOR, LAMP — ^An apparatus used in the central sta- 
tioii of a system of incandescent lamp distrilbution to 
indicate the presence of the proper voltage or potential 
difference on the mains. 

INDICATOR, POTENTIAL— An apparatus for indicating 
the potential difference between any points of a circuit. 

INDICATOR, SPEED— A name sometimes applied to a 
tachometer. A revolution counter. 

INDUCED CURRENT— (See Current, Induced). 



357 IND 

INDUCTANCE — The induction of a current on itself, or on 
other circuits. 

Self-induction. 

A term generally employed instead of self-induction. 

That property in virtue of which a finite electromo- 
tive force, acting" on a circuit, does not imimediately 
generate the full current due to its resistance, 'and 
when the electromotive force is withdrawn, time is re- 
quired for the currenit strength to fall to zero. — (Flem- 
ing.) 

A quality by virtue of which the passage of an elec- 
tric current is necessarily accomipanied by the absorp- 
tion of electric energy in the formation of a magnetic 
field. 

INDUCTANCE, CO-EFFICIENT OF— A constant quantity, 
such that when multiplied by the current strength 
passing in any coil or circuit, w^ill represcmt numerical- 
ly' the induction through the coil or circuit due -to that 
current. 

. A term sometimes used for co-efficient of self-induc- 
tion. 

INDUCTANCE, VARIABLE— The inductance .which occur-, 
in circuits formed partly or w^holly of substances like 
iron or other paramagnetic substances, the magnetic 
permeability of which varies vrith the intenisity of the 
magnetic induction, and where the lines of force have 
their circuit partly or whollj^ in soich material or vari- 
able magnetic permeability. 

INDUCTION — An influence exertea hy a charged body or 
by a magnetic field on neighboring bodies without ap- 
parent communication. 



^ 



IND 



358 



INDUCTION, ELECTRO-DYNAMIC— Electromcytive forces 
set up by induction in conductors which are either ac- 
tually or practically moved so as to but the lines of 
mag-netic force. 

These electromotive forces, v^^hen permitted to act 
through a circuit, produce an eleciric current. 

INDUCTION, ELECTRO-MAGNETIC— A variety of electro- 
dynamic induction in which electric currents are pro- 
duced by the motion of electro-magnetic solenoids. 

INDUCTION, ELECTROSTATIC— The production of an 
electric charge in a conductor brought inito an eleotro- 
static field. 

INDUCTION, MAGNETIC— The production of magnetism 
in a magnetizable subsitance by bringing it into a mag- 
netic field. 

INDUCTION, MAGNETIC, CO-EFFICIENT OF— A term 
sometimes used instead of magnetic permeability. 
(See Permeability, Magnetic). 

INDUCTION, MAGNETIC LINES OF— Lines which show 
not only the direction in which magnetic induction 
takes place, but also the magnitude of the Induction. 
This term is often loosely used for lines of force. 

INDUCTION, MAGNETIC-ELECTRIC— A variety of electro- 
dynamic induction in which electric currents are pro- 
duced by 'the motion of permanent magnets, or of con- 
ductors past permanent magjiets. 

INDUCTION, MUTUACr— Induction produced by two neigh- 
boring circuits on each other by the mutual interaction 
of their magnetic fields. 



359 IND 

INDUCTION, MUTUAL, CC-EFFICIENT OF— The quanti- 
ty which represents the number of lines of force which 
are common to or linked in wi'th -tw^o circuits, which are 
producing mutual induction on each other, 

INDUCTION, REFLECTION OF— A term proposed by 
Flenning to express an action which resembles a reflec- 
tion of inductive power. 

INDUCTION, SELF — Inauction produced in a circuit while 
changing- the current therein iby the induction of the 
current on itself. 

INDUCTION, SELF, CO-EFFICIENT OF— The amount of 
cutting of magnetic lines in any circuit due to the pas- 
sage of unit current. 

For a given coil the co-efficient of self-induction 
is, according to S. P. Thompson: 

(1.) Proportional to the -square of the number of 
convolutions. 

(2.) Is increased by the use of an iron eore. 
(3.) If the magnetic permeability is assumed as con- 
stant, the co-efficient of self-induction is numerically 
equal to the product of the number of lines of magnetic 
force due to the current, and the number of times they 
are enclosed by the circuit. 

INDUCTION, TOTAL MAGNETIC— The total magnetic in- 
duction of any space is the number of lines of magnetic 
induction w^hich pass through that space, where the 
magnetizable material is placed together with the lines 
added by the magnetization of the magnetic material. 

INDUCTION, UNIPOIiATl— A term sometimes applied to 
the induction that occurs when a conductor is so 
moved through a magnetic field as to continuously cut 
its lines of force. 



INK 360 

INDUCTIOXLESS RESISTANCE— (See Resistance, Indue- 
tionless ) 

INDUCTIVE CAPACITY, SPECIFIC— (See Capacity, Speci- 
fic Inductive.) 

INDUCTIVE CIRCUIT— (See Circuit, Inductive.) 

INDUCTIVE RESISTANCE— (See Resistance, Inductive.) 

INDUCTOR DYNAMO— (See Dynamo, Inductor.) 

INDUCTORIUM — A name sometimes applied to a Ruhin- 
korff induction coil. 

INEQUALITY, ANNUAL, OF EARTH'S MAGNETISM- 
Variations in the value of the earth's magnetism dur- 
ing' the earth's revolution depending on the position 
of the sun. 
Annual variations in the earth's magnetism. 

INERTIA — The inability of a body to change its condition 
of rest or motion, unless some force acts on it. 

INERTIA, ELECTRIC- A term sometimes employed in- 
stead of electro-magnetic inertia. 

A term employed to indicate the tendency of a cur- 
rent to resist its stopping or starting. 

INERTIA, MAGNETIC— The inability of a magnetic core 
to instantly lose or acquire magnetism. 

INFLUENCE, MACHINE— (See Machine, Electrostatic In- 
duction.) 

INK WRITKR, TELEGRAPHIC— A device employed for 
recording the dots and dashes of a telegraphic messno-e 
in ink on a fillet or strip of paper. 



361 INT 

INSTALLATION — A term embracing- the entire plant and 
its accessories required to perform any specified work. 
The act of placing*, arranging- or erecting- a plant or 
apparatus. 

INSTALLATION, ELECTRIC— The establishment of any 

electric plant. 
INSULATING STOOL- (See StooL Insulating.) 

INSULATING TAPE— (See Tape, Insulating.) 

INSULATION, ELECTRIC— Non-conducting material so 
placed with respect to a conductor as to prevent the 
loss of a charge, or the leakage of a current. 

INSULATOR, DOUBLE-CUP— An insulator consisting of 
two funnel-shaped cups, placed in an inverted position 
on the supporting pin and insulated from one another 
by a free air space, except near the ends, which are 
cemented. 

INSULATOR, FLUID— An insulator provided with a small, 
internally placed, annular, cup-shaped space, filled with 
an insulating oil, thus increasing the insulating power 
of the support. 

INSULATOR, OIL— A fluid insulator filled with oil. 

INSULATOR TELEGRAPHIC OR TELEPHONIC— A non- 
conducting support of telegraphic, telephonic, electric 
light or other wires. 

INTENSITY, MAGNETIC— Density of magnetic induction. 
INTENSITY OF CURRENT— (See Current, Intensity of.) 
INTENSITY OF FIELD— (See Field, Intensity of.) 
INTENSITY OF MAGNETIZATION— (See Magnetization. 
Intensity of.) 



ISO 362 

fNTBXSITY, PHOTOMETRIC, UNIT OF— (The amounit of 
light produced by a candle that consumes two grains 
of spermaceti wax per minute.) 

INTERRUPTER, AUTOMATIC— An automatic contact 
breaker. 

INTERRUPTER, TUNING-FORK— An interrupter in which 
the successive makes and breaks are produced by the 
vibrations of a tuning-fork or reed. 

INVERSION, THERMO-ELECTRIC— An inversion of the 
thermo-electric electromotive force of a couple at cer- 
tain temperatures. 

IONS — Groups of atoms or radicals which result from ihe 
electrolytic decomposition oi a molecule. 

IONS, ELECTRO-NEGATIVE— The negative atoms, or 
groups of atoms, called radicals, into which the mole- 
cules of an electrolyte are decomposed by electrolysis. 

IONS. ELECTRO-POSITIVE— -The positive atoms, or groups 
of atoms, called radicals, into which the molecules of 
an electrolyte are decomposed by electrolysis. 

IRON-CLAD ELECTRO-MAGNET— (See Magnet, Electro, 
Iron-Clad.) 

IRON CORE, EFFECT OF, ON THE MAGNETIC 
STRENGTH OF A HOLLOW COIL OF WIRE— An in- 
crease in the number of lines of magnetic force, be- 
yond those produced by the current itself, due to the 
opening out of the closed magnetic circuits in the atoms 
or molecules of the iron. 

ISOCHRONISM— Equality of time of vibration or motion. 
A contraction proposed for Joule. 



363 JOI 

J 

JABLOCHKOFF CANDLE— (See Candle, Jablochkoff.) 

JAR, LEYDEN — A condenser in the form of a jar, in 
which the metallic coatings are placed opposite each 
other on the outside and the inside of the jar respec- 
tively. 

JAR, LEYDEN, CAPACITY OF— The quantitj^ of electricity 
a Leyden jar will hold at a given difference of poten- 
tial. 

JAR, LTGHTNING-— A Leydon jar., the coatings of which 
consist of metallic fillings. 

As the discharge passes, an irregular series of sparks 
appear, which somewhat resemble in their shape a 
lightning flash. Hence the origin of the term. 

JAR OF SECONDARY CELT.— The containing vessel in 
which the plates of a single secondary cell are placed. 

JAR, POROUS— A porous cell. 

JAR,UNrT— A small Leyden jar sometimes employed to 
measure approximately the quantity of electricity 
passed into a Leyden battery or condenser. 

JOINT, .\MERTCAN TWIST -A telegraphic or telephoni 
joint in which each of the two wires is twisted aroiind 
the other. 

JOINT, BRITANNIA—A telegraphic or telephonic joint in 
which the wires are laid side by side, bound together 
and subsequentlj^ soldered. 

JOINT, MAGNETIC— The line of junction between two 
separate parts of magnetization material. 



KER 364 

JOINT, SLEEVE— A junction of the ends of conducting- 
wires obtained by passing- ihem through tubes and 
then twisting" and soldering. 

JOINT, TESTING OF—Ascertaining the resistance of the 
insulating material around a joint in a cable. 
A contraction for electrostatic capacity. 

JOULE — The unit of electric energy or work. 
1 joule equals .73732 foot-pounds. 
1 joule per second equals 1 watt. 

The British Association proposed to call one joule 
the work done by one watt in one second. 

K 

K. W. — A contraction for kilo-watt. 

KAOLIN — A variety of white clay sometimes employed for 
insulating purposes. 

KAPP LINES— (See Lines, Kapp.) 

KAETAYEFvT— A kind of insulating material resembling 
fiber. 

KATHION— 'The electro-positive ion, atom or radical into 
which the molecules of an electrolyte Is decomposed 
.by electrolysis. 

KATHO'DAL— Pertaining to the kathode. 

KATHODE — The conductor or plate of an eleci.o-decom- 
position cell connected with the negative terminal or 
electrode of a battery or other source. 

KEEPER OF MAGNET— (See Magnet, Keeper of.) 

KERITE— An insulating material. 



365 KIL 

KEY, DISCHARGE— A key employed to enable the dis- 
charg-e from a condenser or cable to be readily passed 
through a galvanometer for purposes of measure- 
ment. 

KEY, INCREMENT, OF QUADRUPLEX TELEGRAPHIC 
SYSTEM — A key employed to increase the strength of 
the current and so operate one of the dlistant instru* 
ments in a quadruplex system by an increase in the 
strength of the current. 

KEY PLUG — A simple form of key in which a connection 
is readily made or broken by the insertion of a pKig of 
metal between two metallic plates that are thus in- 
troduced into a circuit. 

KEY, REVERSING— A key inserted in the circuit of a gal- 
vanometer for o<btaining deflections of the needle on 
either side of the galvanome'ter scale. 

KEY, REVERSING, OF QUADRUPLEX TELEGRAPHIC 
SYSTEM — A key employed to reverse the direction of 
the current and so operate one of the distant instru- 
naents, in a quadruplex system, by a change in the di- 
rection of the current. 

KEY, SHORT-CIRCUIT— A key which in its normal condi- 
tion short circuits galvanometer. 

KEY, TELEGRAPHIC— The key employed for sending over 
the line the successive makes and breaks that produce 
the dots and dashes of the Morse alphabet, or the de- 
flections of the needle of the needle telegraph. 

KICKING COIL— (See Coil, Kicking.) 

KILOAMPERE— One thousand amperes. 

KILOGRAMME — One thousand grammes, or 2.2046 pounds 
avoirdupois. 



LAG 366 

KILOWATT— One thousand -watts. 

KILOWATT HOUR— (See Hour, Kilowatt.) 

KINETIC ENERGY— (See Energy, Kinetic.) 

KINETOGRAPH — A device for the simultaneous reproduc- 
tion of a distant stage and its actors under circum- 
stances such that the actors can be heard at any dis- 
tance from the theatre. 

KITE, FRANKLIN'S— A kite raised in Philadelphia, Pa., 
in June, 1752, b}^ means of "which Franklin experiment- 
ally demonstrated the identity between lightning and 
electricity, and which, therefore, led to the invention 
of the lightning rod. 

KNIFE, BREAK SWITCH— (See Switch, Knife Break.) 



L — A contraction for co-efficient of inductance. 

L — A contraction for length. 

LAG, ANGLE OF— The angle through which the axis of 
magnetism of the armature of a dynamo-electric ma- 
chine is shifted by reason of the resistance its core 
offers to sudden reversals of magnetization. 

LAG, ANGLE OF, OF CURRENT— An angle <whose tangent 
ds equal to the ratio of the inductive to the ohmic re- 
sistance. 

lAn angle, the tangent of which is equal to the induc- 
tive resistance of the circuit, divided by the ohmic re- 
sistance of the circuit. 

LAG, MAGNETIC— -A magnetic viscosity as manifested by 
the sluggishness with which a magnetizing force pro- 
duces its m-agnetizing effects in iron. 



367 LAM 

LAMINATED CORE— (See Core, Laminated.) 

LAMP, ALL-NIGHT — A term sometimes applied to a 
double-canbon are lamp. 

LAMP, ARC, ELECTRIC— An electric lam.p in which the 
lig'ht is produced by a voltaic arc formed between two 
or more car'bon electrodes. 

LAMP, CHAMBER OF— The glass bulb or chamlber of an 
iiKoandesicing electric lam-p in which the incandescing 
conductor is placed, and in which is maintained a high 
vacuum. 

LAMP, ELECTRIC, ARC, DIFFERENTTAL^An arc lamp 
in 'Which the movements of the oarbons are controlled 
by the differential action of two magnets opposed to 
each other, one of whose coils is in the direct and the 
other in shunt circuit around the carbons. 

LAMP, ELECTRIC, ARC, DOUBLE CARBON-^An electric 
arc lamp provided with two pairs of carbon electrodes, 
so arranged that when one pair is consumed, the cir- 
cuit is automatically completed through the other pair. 

LAMP, ELECTRIC GLOW— A term employed mainly in 
Europe for an incandescent electric lamp. 

LAMP, ELECTRIC, INCANDESCENT- An electric lamp in 
which the light is produced by the electric incandes- 
cence of a strip or filament of some refractory sub- 
stance, generally carbon. 

LAMP, ELECTRIC, INCANDE.SCENT, LIFE OF— The nuui- 
ber of hours that an incandescent electric lamp, when 
traversed by the normal current, will continue to af- 
ford a good commercial light. 




LAW 368 

LAlVfP, ELECTRIC, SAFETY— An incandescent electric 
lamp, >Wth thoroughly insulated leads, employed in 
mines, or other similar places, where the explosive ef- 
fects of readily ignitable substances are to be feared. 

LAMP, ELECTRIC, SERIES CONNECTED INCANDES- 
CENT — An intandescent electric lamp adapted for use 
in series circuits. 

LAMP, ELECTRIC, INCANDESCENT, ELECTRIC FILA- 
MENT OF — A term now generally- applied to the in- 
candescing* conductor of an incandescent electric 
lam]), whether the same be of very small cross-sectlcin 
or of comparativel}^ large cross-section. 

LA^fP, PILOT — In systems for the operation of electric 
lamps, an incandescent lamp emplo^-ed in a station 
to indicate the dilTerence of potenial at the dynamo 
terminals, hy means of the intensity of its emitted 
lig-ht. 

LAMP ROD— (See Rod, Lamp.) 

LAMI'S, BANK OF— A term applied to a number of lamps, 
equal to about half the load^ that were formerly 
placed in view of the attendant in circuit Math a dyna- 
mo that is to be placed in a parallel circuit with 
another dvnamo, one of the lamps of which is also in 
view. 

LAMPS, CARRONING— Placing- carbons in electric arc 
lami)S. 

LAUNCH, ELECTRIC— A boat, the motive power for which 
is electricity, suitable for launching- from a ship. 

LAW, JACOBI'S— The maximum work done by a motor is 
reached when the counter-electromotive force is equal 
to one-half of the impressed electromotive force. 



369 LAW 

LA^/V, JOULE'S — The heating power of a current is pro- 
portional to the product of the resistance and the 
square of the current strength. 

LAW, NATURAL — A correct expression of the order in 
which the causes and eifects of natural phenomena fol- 
low one another. 

LAW OF OHM, OR LAW OF CURRENT STRENGTH- -The 
strength of a continuous current is directly propor- 
tional to the dilference of potential or electromotive 
force in the circuit, and inversely proportional to the 
resistance of the circuit, i. e., is equal to the quotient 
arising from, dividing the electromotive force by the 
resisttance. 

LAW, YOLTAMERIC— The chemical action produced by 
electrol3^sis in any electrolyte is proportional to the 
amount of electricity which pasfrcs through the elec- 
trolyte. 

LAWS, LENZ S — Laws for determining the directions of 
currents produced by eleotrodynamic induction. 

The direction of the currents set up by electrodyna- 
mic induction is always such as to oppose the motions 
by whch such currents were produced. 

LAWS OF COULOMB, OR LAWS OF ELECTROSTATIC 
AND MAGNETIC ATTRACTIONS AND REPULSIONS. 
— Laws for the force of attraction and repulsion be- 
tween charged bodies or between magnet poles. 

Tlie fact that the force of electrostatic attraction or 
repulsion between two charges, is directly proportional 
to the product of the qualities of electricity of the tvvo 
charges and inversely proportional to the square of the 
distance between them, is known as Coulomb's Law. 



LEG 



370 



LAWS or JOULE — Laws expressing the development of 
heat produced in a circuit by an electric current. 

LEAD, ANGLE OF — The angular deviation from the nor- 
mal position, which must be given to the collecting 
brushes on the commutator cylinder of a dynamo-elec- 
tric machine, in order to avoid destriiolive burning. 

LEAD OF BRUSHES OF DYNA:NLO-ELECriaC MACHINE 
— The angular deviation from the normal position, 
which it is necessary .to give the brushes on Ihe com- 
mutator of a dynamo-elect lie machine, in order to ob- 
tain i fTn ient action. 

LEADING HORN OF POLE PIECES OF DYNAIMO-ELEC- 
TEIC MACIIINE— (See Horns, Leading, of Pole Pieces 
of a Dynamo-Electric Machine). 

LEADING-IN WIRES— (See Wires, Leading-In). 

LEADS — The conductors in any system of electric distribu- 
tion. 

LEAKAGE, ELECTRIC— The gradual dissipation of a cur- 
rent due to insufficient insulation. 

LEAKAGE. MAGNE'i ...— A useless dissipation of the lines 
of magnetic force of a dynamo-electric machine, or 
other similar device, by Their fail«ire to pass through 
the armature where they are needed. 

Useless dissipation of lines of magnetic force outside 
that portion of the field of a dynamo-electric machine 
through w^hich the armature moves. 

LECL.\NCHE'S VOLTAIC CELL— (See Cell, Voltaic, Le- 
clanche). 



371 LIG 

LEG — In a system of telephonic exchange, where a ground 
return js used, a single wire, or, where a metallic cir- 
cuit is employed, two wires, for connecting a subscriber 
with the main switchboard, by means ot which any 
subscriber may be legged or placed directly in circuit 
w-ith two or more other parties. 

LEGAL OHM— (See Ohm, Legal). 

LENGTH OF SPAEK— (See Spark, Length of). 

LENZ'S LAW— (See Law, Lenz's). 

LEYDEN JAR Bx\TTERY— (See Battery, Leyden Jar). 

LIGHT, ELECTRIC— Light produced by the action of elec- 
tric energy. 

LIGHT, MAXWELL'S, ELETRO-MAGNETIC THEORY OF 
— A hypothesis for the cause of light produced by Max- 
w^ell, based on the relations existing between the phe- 
nomena of light and those of electro-magnetism. 

LIGHT, SEARCH, ELECTRIC— An electric arc light placed 
in a focusing lamp before a lens or mirror, so as to ob- 
tain either a parallel beam or a slightly divergent pen- 
cil of light for lighting the surrounding space for pur- 
poses of exploration. 

LIGHTER, CIGAR, ELECTRIC— An apparatus for electric- 
ally lighting a cigar, 

LIGHTING, ARC— Artificial illumination obtained by 
means of an arc light. 

The term arc lighting is used in contradistinction to 
incandescent lighting. 

LIGHTING, ELECTRIC, CENTRAL STATION— The light- 
ing of a number of houses or other buildings from a 
single station, centrally located. 



LIG 372 

LIGHTING, ELECTEIC GAS— Igniting gas jets by means 
of electric discharges. 

IIGHTiyG, ELFXTRIC, ISOLATED— A system of electric 
lighting where a separate electric source is placed in 
each house or area to be lighted, as distinguished from 
the central station lighting, where electric sources are 
provided for the production of the current required for 
an entire neighborhood. 

LIGHTNTXC— The spark ox bolt that results from the dis- 
ruptive discharge of a cloud to the earth, or to a neigh- 
boring cloud. 

LIGHTNING AEKESTER— (See Arrester, Lightning). 

LIGHTNING, BACK-STROKE OF— An electric discharge, 
caused by an induced charge, which occurs after the 
direct discharge of a lightning flash. 

LIGHTNING, CHAIN— A variety of lightning flash in which 
the discharge takes a rippling path, somewhat resem- 
bling a chain. 

LIGHTNING, FORKED—A variety of lightning flash, in 
which the discharge, on nearing the earth or other 
object, divides into two or more branches. 

LIGHTNING, GLOBULAR— A rare form of lightning, in 
which a globe of Are appears, which quietly floats for a 
while in the air and then explodes with great violence. 

LIGHTNING, HEAT— A variety of lightning flash in which 
the discharge lights up the surfaces of the neighboring 
clouds. 

LIGHTNITs^G, SHEET— A variety of lightning flash unac- 
companied by any thunder audible to the observer, in 
which the entire surfaces of the clouds are illuminated. 



373 LIN 

LIGHTNING, VOLCANIC— The lightnino' discharges that 
attend most volcanic eruptions. 

LIGHTNING, ZIGZAG— The commonest variety of light- 
ning* flashes, in w^hich the discharge apparently as- 
sumes a forked zigzag, or even a chain-shaped path. 

LINE-- -A wire or other conductor connecting any two 
points or stations. 

LINE, AERIAL — An air line as distinguished from an un- 
derground conductor, 

LINE, AKITFICIAL — A line so made up by condensers and 
resistance coils as to have the same inductive eltects 
on charging or discharging as an actual telegraph line, 

LINE, CAPACITY OF— The ability of a line or cable to act 
like a condenser, and therefore like it to possess a ca- 
pacity. 

LINE CIRCUIT— (See Circuit, Line). 

LINE, NEUTRAL, OF A MAGNET— A line joining the neu- 
tral points of a magnet or points approximately mid- 
way betw^een the poles. 

LINE, NEUTRAL, OF COMMUTATOR CYLINDER—A line 
on the commutator cylinder of a dynamo-electric ma- 
chine connecting the neutral points, or the points of 
maximum positive and negative difference of potential. 

LINEMAN — One w^ho puts up and repairs line circuits and 
attends to the devices connected therewitJi. 

LINES, KArP— A term proposed by Mr. Gisbert Kapp for 
a unit of lines of magnetic force. 
One Kapp line equals 6,000 C. G. S. magnetic lines. 



LOG 374 

LINES OF FOPiCE, CUTTING-- (See Force, Lines of, Cut- 
ting). 

LINES OF FORCE, DIRECTION OF— (See Force, Lines of, 
Direction of). 

LINES OF MAGNETIC FORCE— (See Force, Magnetic, 
Lines of). 

LINES, OVERHEAD— A term applied to telegraph, tele- 
phone and electric light or power lines that run over- 
head, in contradistinction to similar lines placed un- 
derground. 

LINKS, FUSE— Strips or plates of fusible metal in the form 
of links, employed for safety fuses for incandescent or 
other circuits. 

LIQUID, ELECTROPOION— A battery liquid consisting of 
1 pound of bichromate of potash dissolved in 10 pounds 
of vrater, to which 2Vo pounds of commercial sulphuric 
acid has been gradually added. 

LIQUID, EXCIXING, OF VOLTAIC CELL The electro- 

Ij^te or liquid in a voltaic cell, which acts on the posi- 
tive plate. 

LOAD, LIQUID RESISTANCE— An artificial load for- a 
dynamo-electric machine, consisting of a mass of liquid 
interposed between electrodes. 

LOCAL BATTERY— (See Battery, Local). 

LOCOMOTIVE, ELECTRIC— A railway engine whose mo- 
tive power is electricity. 

LOCO^rOTIVE HEAD LIGHT, ELECTRIC— (See Head 
Light, Locomotive). 



375 MAO 

LODE ST ONE— A name formerly applied to an ore or iron 
(magnetic iron ore), that naturally possesses the power 
of attracting jneces of iron to it. 

LOOP, ELECTEIC — A portion of a main circuit consisting 
of a wire going* out from one side of a break in the 
main circuit and returning to the other side of the 
break. 

M 

MACHINE, AEMSTEONG'S HYDRO-ELECTIilC— A ma- 
chine for the development of electricity by the friction 
of a jet of steam passing over a water surface. 

MACHINE, DYNAMO-ELECTRIC— A machine for the con- 
version of mechanical energy into electrical energy, by 
means of magneto-electric induction. 

MACHINE, D YNA MO-ELECTRIC, ALTERNATING-CUR- 
RENT — A dynamo-electric machine in which alternat- 
ing currents are produced. 

MACHINE, DYNAMO-ELECTRIC, BI-POLAR— A dynamo- 
electric machine, the armature of which rotates in a 
field formed by two magnet poles, as distinguished 
from a machine the armature of which rotates in a field 
formed by more than two magnet poles. 

Mi\ CHINE, DYNAMO-ELECTRIC, CLOSED-COIL— A dyna- 
mo-electric machine, the armature coils of which are 
grouped in sections, communicating with successive 
bars of a collector, so as to be connected continuously 
together in a closed circuit, 

MACHINE, DYNAMO-ELECTRIC, CLOSED-COIL DRUM— 
A closed-coil dynamo-electric machine, the armature 
core of which is drum-shaped. 



MAO 376 

MACHINE DYNAMO-ELECTRIC, CLOSED-COIL RING— A 
closed-coil dynanio-eleclric machine, the armature 
core of which is ring-shaped. 

M\CHINE, DYNAMO-ELECTRIC, COMPOUND-WOUND— 
Machines whose field mai^nets are excited by more than 
one circuit of coils, or by more than a sing-le electric 
source. 

MACHINE, DYNAMO-ELECTRIC, CONTINUOUS-CUR- 
RENT — A dynamo-electric machine, the current of 
which is commuted so as to flow in one and the samo 
direction, as distinguished from an alternating dynamo. 

MACHINE, DYNAMO-ELECTRIC, EFFICIENCY OF— The 
ratio between the electric energy or the electrical 
horse-power produced by a dynamo, and the mechani- 
cal energy or horse-power expended in driving the 
dynamo. 

MACHINE, DYNAMO-ELECTRIC, FLASHING OF— A name 
given to long flashing sparks at the commutator, due to 
the short circuiting of the external circuit at the com- 
mutator, by arcing over the successive commutator in- 
sulating strips. 

MACHINE, DYN.\MO-ELECTRIC, MLTLTIPOLAR— A dyna- 
mo-electric machine, the armature of which revolves 
in a field formed by more than a single pair of poles. 

MACHINE, DYNAMO-ELECTRIC, OPEN-COIL— A dynamo- 
electric machine, the armature coils of which, though 
connected to the successive bars of the commutator, 
are not connected continuously in a closed circuit. 

MACHINE, DYNAMO-ELECTRIC, OPEN-COIL RING— An 
open-coil dynp.mo-electric machine, the annature core 
of which is ring-shaped. 



377 MAC 

MACHINE, DYNAMO-ELECTRIC, REVERSIBILITY OF— 
The ability of a dynamo to act as a motor when trav- 
ersed by an electric current. 

MACHINE, DYNAMO-ELECTRIC, SEPARATELY EXCIT- 
ED — A dynamo-electric machine in which the field 
mag'net coils have no connection with the armature 
coils, but receive their currertt from a separate machine 
or source, 

MACHINE, DYNAMO-ELECTRIC, SERIES-WOUND— A 
dynamo-electric machine, in wliich the field circuit and 
the external circuit are connected in series with the 
armature circuit, so that the entire armature current 
must pass through the field coils. 

MACHINE, DYNAMO-ELECTRIC, SHUNT-WOUND— A 

dynamo-electric machine in which the field magnet 
coils are placed in a shunt to the armature circuit, so 
that only a portion of the current generated passes 
through the field magnet coils, but all the difference of 
potential of the armature acts at the terminals of the 
field circuit. 
MACHINE, DYNAMO-ELECTRIC, SINGLE-MAGNET— A 
d3^namo-electric machine, in which the field magnet 
poles are obtained by means of a single coil of insulated 
wire, instead of by more than a single coil. 

MACHINE, DYNAMO-ELECTRIC, SPARKING OF— An ir- 
regular and injurious operation of a dynamo-electric 
machine, attended with sparks at the collecting 
brushes. 

MACHINE, DYNAMO-ELECTRIC, TO SHORT CIRCUIT A 
— To put a dynamo-electric machine on a circuit of 
comparatively^ small electric resistance. 



MAC 378 

MACHTNF, ELECTROSTATIC INDUCTION—A machine in 
which a small initial charsre produces a greatly increas- 
ed charge hy its inductive action on a rapidly rotated 
disc of glass or other dielectric. 

M/. CHINE, FKICTIONAL ELECTRIC— A machine for the 
development of electricity by friction. 

MACniNE, HOLTZ— A particular form of electrostatic in- 
duction machine. 

MACHINE, INDUCTOR— An alternating current dynamo in 
w^hich the field magnet projections are all of ihe same 
polarity. 

MACHINE, MAGNETO BLASTING— A magneto-electric 
machine employed for generating the current used in 
electric blasting. 

MACHINE, MAGNETO-ELECTRIC— A machine in \vhich 
there are no field magnet cOils, the magnetic field of 
the machine being due to the action of permanent steel 
magnets. 

MACHINE, RHEOSTATIC— A machine devised by Plante 
in vrhich continuous static efl'ects of considerable in- 
tensity are obtained by charging a number of condens- 
ers in multiple-arc and discharging them in series. 

MACHINE, TOPPLER-HOLTZ— A modified form of Holtz 
machine in which the initial charge of the armatures 
is obtained by the friction of metallic brushes against 
the armatures. 

MACIITNE, WIMSHITRST ELECTRICAL— A form of con- 
vection electric machine invented by Wimshurst. 



379 MAG 

MAGNET — A body possessing the power of attracting' the 
unlike pole of another mag-net or of repelling- the like 
pole; or of attracting readily magnetizable bodies like 
iron filings to either pole. A body possessing* a mag- 
netic Held. 

MAGNET, ARTIFICfAL— A magnet produced by induction 
from another magnet, or from an electric current. 

MAGNET, COMPOUND— A number of single magnets, 
placed parallel and with theiT similar poles facing one 
another. 

MAGNET, DAMPING— Any magnet employed for the pur- 
pose of checking the velocity of motion of a moving 
body or magnet. 

MAGNET, ELECTING- A magnet produced by the passage 
of an electric current through a (!oil of insulated wire 
surrounding a core of magnetizable material. 

MAGNET, ETECTEO, HOKSESHOE— An electro-magnet, 
the core of which is in the shape of a horseshoe or U. 

MAGNET, ELECTKO, HUGHES'— An elecfro-magnet in 
which a U-shaped permanent magnet is provided with 
pole pieces of soft iron, on which only are placed the 
n^iagnetizing coils. 

A quick-acting electro-magnet, in which the magnet- 
izing coils are placed on soft iron pole pieces that are 
connected with and form the prolongations of fTie poles 
of a permanent horseshoe magnet. 

MAGNET, ELECT'EO, IKON-CLAD— An electro-magnet 
whose magnetizing coil is almost entirely surrounded 
by iron. 

MAGNET, HOKSESHOE— A magneiized bar of steel or iron 
bent in the form of a horsesihoe or letter U. 



MAG 380 

MAGNET, IRON-CLAD— A mag-net who've mag-nettc resist- 
ance is lowered by a casing" of iron connected with the 
core and provided for the passage of the lines of ning*- 
netic force. 

MAGNET, KEEPER OF— A mass of soft iron applied to the 
poles of a magnet through which its lines of magnetic 
force pass. 

M\GNET, PERMANENT— A magnet of hardened steel or 
other paramagnetic substance wihich retains its mag- 
netism for a long time after being magnetized. 

MAGNET, PORTATIVE POWER OF— The lifting power of 
a magnet. 

MAGNET, RELAY — ^An electro-magnet, whose coils are 
connected to the main line of a telegraphic circuit, and 
the movem.ents of whose armature is employed to bring 
a local battery into action at the receiving station, the 
current of which operates the register or sounder, 

MAGNET, FIELD, OF DYNAMO-ELECTRIC MACHINE— 
One of the electro-magnets employed to produce the 
magnetic field of a dynamo-electric machine. 

MAGNETIC ATTRACTION— (See Attraction, Magnetic). 

MAGNETIC CIRCTTIT— (See Circuit, Magnetic). 

MAGNETIC DENSITY— (See Density, Magnetic). 

MAGNETIC FIELD -(See Field, Magnetic). 

MAGNETIC T EAKAGE— (See Leakage, Magnetic). 

MAGNETIC LINES OF FORCE— CSee Force. Magnetic 
Lines of). 

MAGNETIC POLES— (See Poles, Magnetic). 



881 MAG 

MAGNETIC "RELUCTANCE— (See Reluctance, Ma^rnetic). 
MAGNETIC EESTSTANCE— (See Pvesistance, Magnetic). 
MAGNETIC STOPiM— (See Storm, Magnetic). 

MAGNETIC WHTP.L- (See Whirls, Magnetic), 

MAGNETISM—That branch of science ^^4lich treats of the 
nature and properties of magnets and the magnetic 
field. I 

MAGNETISM, AMPERE'S THEORY OF— A theory or hypo- 
thesis proposed by Ampere, to account for the cause of 
magnetism, by the presence of electric currents in the 
ultimate portiolos of matter. 

MAGNETISM, ELECTRO— Magnetism produced by means 
of electric currents. 

MAGNETISM, EWING'S THEORY OF— A theory of mag- 
netism proposed by Prof. Ewing, based on the assump- 
tion of originally magnetized particles. 

MAGNETISM, HUGHES' THEORY OF— A theory pro- 
pounded by Hughes to account for the phenomena oi 
magnetism apart from the presence of electric currents. 

MAGNETISM, RESIDUAL— The magnetism remaining in 
the core of an electro-magnet on the opening of the 
magnetizing circuit. 

The smqll amount of magnetism retained by soft 
iron when removed from any magnetizing field. 

MAGNETISM, STRENGTH OF— A term sometimes used in 
the sense of intensity of magnetization. 

MAGNETIZABLE— Capable of being magnetized after the 
manner of a paramagnetic substance like iron. 



MAI 



382 



MAGNETIZATION— The act of calling- out or of endo\\dng 
with ina<>-netic properties. 

M\GNETIZATION, INTENSITY OF— A quantity showing 
the intensity of the magnetization produced in a sub- 
stance. A quantity sho^ving the intensity with which a 
raagnetizable substance is magnetized. 

MAGNETIZATION, TIME-LAG OF— A lag which. appear*; 
to exist between the time of action of the magnetizing 
force and the appearance of the magnetism. The time 
which must elapse in the case of a given paramagnetic 
substance before a magnetizing force can produce mag- 
netization. 

MAGNETIZE — To endow with magnetic properties. 

MAGNETO-ELECTPvIC BELL— (See Bell, Magneto-Electric) 

MAGNETO-ELECTRIC BRAKE— (See Brake, Magneto- 
Electric). 

I^IAGNETOMETER— An apparatus for the measurement of 
magnetic force. 

MAGNETO-MOTIVE FORCE— (See Force, Magneto-Motive) 

MAIN, ELECTRIC — The principal conductor in any system 
of electric distribution. 

!\[AIN, HOUSE — A term employed in a system of multiple 
incandescent lamp distribution for the conductor con- 
necting the house service conductors with a center of 
distribution, or with a street main. 

MAIN, STREET — In a system of incandescent lamp distri- 
bution the conductors extending in a system of net- 
works through the streets from junction box to june- 
tion box, through which the current is distributed from 
the feeder ends, through cut-outs, to the district to be 
lighted, and from which ser^dce wires are taken. 



383 MET 

MAKE-AND-BREAK, AUTOMATIC— A term sometimes em- 
ployed for siieh a combination of contact points with 
the armature of any electro-magnet, that the circuit is 
automatically made and broken with great rapidity. 

MAErS'EK'S COMPASS— (See Compass, Azimuth). 

MATERIALS, INSULATING— Ts^on-conducting- substances 
which are placed around a conductor, in order that it 
may either retain an electric charge, or permit the pas- 
sage of an electric current through the conductor with- 
out sensible leakage. 

MATTING, INVISIBLE ELECTBIC FLOOB— A matting or 
other iloor covering, provided vrith a series of electric 
contacts, which are closed by the passage of a person 
walking over them, 

MEDIUM, ELECT'BO-MAGNETIC— Any medium in which 
electro-magnetic phenomena occur. 

MEG OB MEGA (as a prefix)— 1,000,000 times; as, megohm, 
1,000,000 ohms; megavolt, 1,000,000 volts. 

MEGOHM— 1,000,000 ohms. 

METALLIC CIBCUIT— (See Circuit, Magnetic). 

METALLOID — A name formerly applied to a non-metallic 
body, or to a body having only some of the properties 
of a metal, as carbon, boron, oxygen, etc. 

METALLUBG Y, ELECTBO— That branch of applied science 
which relates to the electrical reduction or treatment 
of metals. Metallurgical processes effected by the 
agency of electricity. 

METEB, AMPEBE— (Sec Ampere-Meter. Ammeter). 



1 



MIC 384 

METEE, CUHRENT— A term now applied to an electric 
meter or galvanometer which measures the current in 
amperes, as distinguished from one which measures 
the energ'y in watts. 

METER, ETiECTr.TC— Any apparatus for measuring com- 
mercially the quantity of electricity that passes in a 
given time through any consumption circuit. 

METER, ELECTRO-CHEMICAL— An electric meter in 
w^hich the current passing is measured by the electro- 
lytic decomposition it effects. 

METER, ELECTRO-MAGNETIC— An electric meter In 
which the current passing is measured by the electro- 
magnetic effects it produces. 

METER, ENERGY— A term sometimes applied to a watt 
meter. 

METER, MILLI- AMPERE— An ampere meter graduated to 
read milli-amperes. 

METER, WATT — An instrument generally consisting of a 
galvanometer constructed so as to measure directly the 
prodi^ct of the (;urrent, and the difference of potential. 

MHO — A ferm proposed by Sir Wm. Thomson for the prac- 
tical unit of conductivit\ . Such a unit of conductivity 
as is equal to the reciprocal of 1 ohm. 

MICA — A mineral substance employed as an insulator. 

MICA, MOULDED— An insulating substance consisting ot 
finelj^ divided mica made into a paste, with some fused 
insulating substance, and moulded into any desired 
shape. 



385 MOR 

MICRO (as a prefx) — The one-millionth; as, a microfarad, 
the millionth of a farad; a microvolt, the one-millionth 
of a volt. 

MICEO-FAEiVD— (See Farad, Micro). 

MTCPtOPHONF — An apparatus invented by Prof. Hng-hes 
for rendering faint or distant sounds distinctly audible. 

MIL — A unit of length equal to the 1-1000 of an inch, or .001 
inch, used in measuring the diameter of wires. 

MIL, CIRCLTLAR — A unit of area emrjloyed in measuring 
the areas of cross-sections in wires, equal to .78540 
square mil. The area of a circle one mil in diameter. 

MIL, SQUARE — A unit of area employed in measuring the 
areas of cross-sections of wires, equal to .000001 square 
inch. One square mil equals 1.2732 circular mil. 

MTLLI (as a prefix) — The one-thousandth part. 

MILLI-AMPERE— The thousandth of an ampere. 

MINE, ELECTRO-CONTACT— A submarine mine that is 
fired automatically on the completion of the current 
of a battery placed on the shore through the closing of 
floating contact points by passing vessels. 

MIRROR GALVANOMETER— (See Galvanometer, Mirror). 

MORSE ALPHABET— (See Alphabet, Telegraphic: Morse's) 

MORSE RECORDER— (See Recorder, Morse). 

MORSE SYSTEM OF TELEGRAPHY— (See Telegraphy, 
Morse System of). 

MORSE'S TELEGRAPHIC ALPHABET— (See Alphabet, 
Telegraphic: Morse's). 



yr 



MOT 



386 



MOTION, SIMPLE-HARMONIC— ]\rotion which repeats it- 
self at reg-iilar intervals, taking- place backwards or 
forwards, and which may be studied by comparison 
with nniform motion round a circle of reference. 

MOTOGRAPH, ELECTRO— A land speaking telephone in- 
vented by Edison whereby the friation of la platinum 
point ag-ainst a rotating cylinder of moist chalk, is re- 
duced by the passag-e of an electric current. 

MOTOR, COMPOUND-WOUND— An electric motor whose 
field magnets are excited by a series and a shunt wire. 

:M0T0R, ELECTRIC— a device for transforming electric 
power into mechanical power. 

MOTOR, ELECTRIC, VLTERNATING-CURRENT— An elec- 
tric motor driven or operated by means of alternating 
currents. 

MOTOR, ELECTRIC, DIRECT-CURRENT— An electric m.o- 
tor driven or operated by means of direct or continuous 
electric currents, as distinguished from a motor driven 
or operated b}' alternating currents. 

MOTOR, ELECTRIC, SLOW-SPEED— An electric motor so 
constructed as to run with fair efficiency at slow speed. 

MOTOR, PYROMAGNETIC— A motor driven by the attrac- 
tion of magnet poles on a movable core of iron or nickel 
unequally heated. 

MOTOR, ROTATING-CURRENT— An electric motor design- 
ed for use with a rotating electric current. 

MOTOR, SERIES- WOUND— An electric motor in which the 
field and armature are connected in series with the 
external circuit as in a series dynamo. 



387 NEE 

MOTOR, SHUNT- WOUND— An electric motor in which the 
field magnet coils are placed in a shunt to the armature 
circuit, 

MULTIPHASE CURRENT— (See Current, Multiphase). 
:^rUI.TIPHASE DYNAMO— (See Dynamo, A[ultiphase). 
MULTIPHASE SYSTEM— CSee System, Multiphase). 
]\rULTIPLE-SEEIES— A multiple counection of series 
g-roups. 

N 

N. — A contraction employed in mathematical writings for 
the whole number of lines of magnetic force in any 
magnetic circuit. 

N. — A contraction for North Pole. 

NEEDLE, ASTATIC— A compound magnetic needle of great 
sensibility, possessing little or no directive power. 

An astatic needle consisting of two separate magnet- 
ic needles, rigidly connected together and placed par- 
allel and directly over each other, with opposite poles 
opposed. 

NEEDLE, MA.CNETIC— A straight bar-shaped needle of 
magnetized steel, poised near or above its center of 
gravit}^ and free to move either in a horizontal plane 
only, or in a vertical plane only, or in both. 

NEEDLE, MAGNETIC, DA]NrPED— A magnetic needle so 
placed as to quickly conie to rest after it has been set 
in motion. 

NEEDLE, MAGNETIC, DECLINATION OF-The angular 
deviation of the magnetic needle from the true geo- 
graphical north. The variation of the magnetic needle. 



Y 



NIC 



388 



NEEDLE, MAGTs^E'HC, DEFLECTION OF— The movement 
of a needle out of a position of rest in the earth's mag- 
ne1ic field or in the field of another magnet, by the 
action of an electric current or another ifiag-net. 

NEEDLE, MAGNETIC, DIPPING— A magneic needle sus- 
pended so as to be free to move in a vertical plane, em- 
ployed to determine the angle of dip or the magnetic 
inclination. 

NEEDLE, MAGNETIC, DIRECTIVE TENDENCY OF— The 
tendency' of a magnetic needle to ino^e so as to co^ne 
to rest in the direction of the lines of the earth's mag- 
netic field. 

NEEDLE, TELEGPAPiriC— A needle employed in teTegr^a- 
phy to represent by its movements to the left or right 
respectively the dots and dashes of the MorSe alphabet. 

NEGATIVE ELECTEODE-(See Electrode, Negative). 

NEGATIVE ELEIMFNT OF A VOLTAIC CELL— (See Ele- 
ment, Negative, of a Voltaic Cell). 

NEGATIVE FEEDERS— (See Feeders, Negative). 

NEGATIVE POLE-- (See Pole, Negative). 

NEUTRAL FEEDER— The feeder that is connected with 
the neutral or intermediate terminal of the dynamos 
in a three-wire system of distribution. 

NETTTRAL LINE OF COM^TUTATOR CYLINDER— (See 
Line, Neutral, of Commutator Cylinder). 

NEUTRAL POINT— (See Point, Neutral). 

NEUTRAL POINTS OF DYNAMO-ELECTRIC MACHINE— 

(See Points, N(?utral, of Dynamo-Electric Machine). 
NICKEL-PLATING— (See Plating, Nickel). 



V 

3^ 



389 OIL 

NO X-CONDUCTORS— Substances that offer so great resist- 
ance to the passage of an electric current through their 
mass as to practically exclude a discharge passing 
through them. 



OHM — The unit of electrical resistance. 

Such a resistance as would limit the flow of electric- 
ity under an electromotive force of one volt to a cur- 
rent of one ampere, or to one coulomb per second. 

OIIM, B. A.- -A contraction for British Association ohm. 

OHM, BOARD OF TRADE— A unit of resistance as deter- 
mined by a committee of the English Board of Trade. 

OHM, BRITISH ASSOCIATION— The British Association 
unit of resistance, adopted prior to 1884. 

OHM, LEG AT. — The resistance of a column of mercury 1 
square millimetre in area of cross-section, and 106 centi- 
metres in length, at the temperature of degree C. or 
3*c degrees F, 

OHM, MEG— One million ohms. 

OHMIC RESISTANCE— (See Resistance, Ohmic or True). 

OHMMETER — A commercial galvanometer, devised by Ayr- 
ton, for directly measuring by the defleclion of a mag- 
netic needle, the resistance of any part of a circuit 
through which a strong current of electricity. isflowing. 

OHM'S LAW— (9ee Law of Ohm). 

OIL INSULATOR— (See Insulator, Oil). 

OIL TRANSFORMER— (See Transformer, Oil). 



PAK 



390 



OPEN-CIRCUIT VOLTAIC CELL-(See Cell, Voltaic, Opeu- 
Circuit). 

OPEN-CIPtCUITED— Put on an open circuit. 

OPEN-COIL BPUM DYNAMO-ELECTPIC MACHINE— (See 
Machine, Dynamo-Electric, Open-Coil Drum). 

OSCILLATIONS, ELECTPIC— The series of partial, inter- 
mittent dischar.o-es of which the apparent instantane- 
ous discharg-e of a Leyden jar through a small resist- 
ance actually consists. 

OSMOSE, ELECTKTC— A ditference of liquid level between 
two liquids on opposite sides of a diaphragm produced 
by the pacsao-e of a strong* electric current through the 
liquids between two electrodes placed therein. 



P. D. OR p. d. — A contraction frequently employed for dif- 
ference of potential. 

PACINOTTT RING- (See Ring-, Pacinotti). 

PAIR, ASTATIC — A term sometimes applied to an astatic 
couple. 

PAPAP'FINE — A name given to various solid hydrocarbons 
of the marsh gas series, that are derived fiom coal or 
petroleum by the action of nitric acid. 

PARAMAGNETIC — Possessing properties ordinarily recog- 
nized as magnetic. Possessing the power of concen- 
trating the lines of magnetic force. 

PARAMAGNETISAT— The magnetism of a paramagnetic 
substance. 



^ 



391 PHA 

PEITIEE EFFECT'— (See Effect, Peltier). 

PENDANT, ELECTRIC— A hanging- fixture provided with a 
socket for the support of an incandescent lamp. 

PENDANT, FLEXIBLE ELECTEIC LTCmT— A pendant for 
an incandescent lamp formed by the flexi"5Te conductors 
which support the lamp. 

PENDULUM, ELECTRIC— A pendulum, so arrang-ed thai its 
♦to-and-fro ttnortdon send electric impulse® over a line, 
either by making* or breaking contacts. 

PERIODIC CURRENT, POWER OF— The rate of transform- 
ation of the energy of a circuit traversed by a simple 
■ periodic current. 

PERIODICITY— The rate of cham-ge in the alterations or 
pulsations of an electric current. 

PERMANENT MAGNET VOLTMETER— (See Voltmeter, 
Permanent Magnet). 

PERMEABILITY CURVE— (See Curve, PermeabiUty). 

PERMEABILITY, MAGNETIC— Conductibility for lines of 
magnetic force. 

The ratio existing between the magnetization pro- 
duced, and the magnetizing force producing such ma^;"- 
netization. 

PERMEAMETER— An apparatus devised by S. P. Thomp- 
son for roughly measuring ihe magnetic permeability}'. 

PHASE, ANGLE OF DIFFFRENCE OF, BETWEEN AL- 
TERNATING CURRENTS OF SAME PERIOD- The 
angle w^hich measures the shifting of phase of a simple 
periodic current with respect to another due to lag or 
other cause. 



PHO 



392 



PHASE, SHIFTING OF, OF AT.TERNATING CURRENT— 
A change in pJiase of current due to magnetic lag or 
other causes. 

PHONE — A term frequently used for telephone. 

PHONOGRAIM — A record produced by the phonograph. 

PHONOGRx\PIi — An apparatus for the reproduction of ar- 
ticulate speech, or of sounds of any character, at any 
indefinite time after their occurrence, and for any 
niiuiber of times. 

PHOSPHORESCENCE, . ELECTRIC — Phosphorescence 
caused in a substance b}^ the passage of an electric dis- 
charge. 

PHOSPHORESCENCE, PHYSICAL— Phosphorescence pro- 
duced in matter by the actual impact of light waxx^s 
resulting in a vibratory motion of the molecules of suf- 
ficient rapidity to cause ^hem to emit light. 

PHOSPHORUS— ELECTRIC S^fELTIXG OF— An electric 
process for the direct proc^uction of phosphorus. 

PHOTOMETER — An apparatus for measuring the Intensity 
of the light emitted by an^^ luminous source. 

PHOTOMETER. ACTINIC— A photometer in which the in- 
tensity of any light is measured b^^ the amount of 
chemical decomposition it effects. 

PHOTOMETER, DISPERSION— A photometer in which the 
light to be measured is decreased in intensity a known 
amount so as to more readily permit it to be compared 
with a standard light of much smaller intensity. 

PIIOTO^IETER, SHADOW- A photometer in which the in- 
tensity of the light to be measured is estimated by a 
comparison of the distances ai which it and a standard 
light produce a shadow of The same intensity. 



393 PIT 

PHOTOMETER, TEANSLUCENT DISC— A pho'tometer in 
which the light to be measured is placed on one side of 
a partly translucent and partly opaque disc, and a 
standard candle is placed on the opposite side, and the 
intensity of the light esttmated by the distances of the 
light from the disc when an equal illumination of all 
parts of the disc is obtained. 

PHOTOPHONE— An instrument invented by Bell for the 
telephonic transmission of articulate speech along a 
ray of light instead of along a conducting wire. 

PIECES, POLE, OF DYNAMO-ELECTRIC MACHINE— 
Masses of iron connected with the poles of the field 
magnet frames of dynamo-electric machines, and shap- 
ed to con form to the outline or contour of the armature. 

PILE, DRY — A voltadc pile or battery consisting of nu- 
merous, cells, the voltaic couple in each of which con- 
sists of sheets of paper covered with zinc-foil on one 
disc and black oxide of manganese on the other. 

PILE, THERMO, DIFFERENTIAL— A thermopile in 
which the tw-o opposite faces are exposed to the 
action of two nearly equal sources of heat in order to 
determine accurately the differences in thermal in- 
tensities of such sources of heat. 

PILE, THERMO-ELECTRIC— A number of separate ther- 
mo-electric couples, united in series, so as to form a 
single thermo-electric source. 

PILOT LAMP— (See Lamp, Pilot.) 

PIN, INSULATOR— A bolt by means of which an insulator 

is attfiched to the telegraphic support or arm. 
PITH BALL- (See Balls, Pith.) 



PLA 



394 



PLANE, PROOF — A small insulated conductor employed 
to take test charg-es from the surfaces of insulated, 
charged conductors. 

PLAT — -A word sometimes used for installation, or for the 
.ipparntus required to carry on any manufacturing 
operation. 

PLANTS, ELECTRICITY OF— Electricity produced natur- 
ally by plants during* their vigorous growth. 

PLATE. NEGAIIVF, OF STORAGE CELL— Tliat place of 
a storage cell which, by the action of the charging 
current, is converted iuto or partly covered with a 
coating of spongy lead. 

PLATE, NEGATIVE, OF VOLTAIC CELL— The electro- 
negative eleruent of a voltaic couple. 
That element of a voltaic couple which is negative in 
the electrolyte of the cell. 

PLATE, POSITIVE, OI' STORAGE PATTERN— That plate 
of a storage battery which is converted into, or 
covered by, a layer of lead peroxide, by the action of 
tlie charging current. 

That plate of storage battery which is connected 
with the positive terminal of the charging source and 
which is, therefore, the positive pole of the battery 
on discharging. 

PLATE, POSITIVE, OF VOLTAIC CELT..— The electro- 
positive in the electrolyte of the cell. 

PLATES OF SECONDARY OR STORAGE CELL, FORM- 
ING OF— Obtaining a thick coating of lead peroxide 
on the lead plates of a storage battery, by repeatedly 
sending the charging current through the cell alter- 
nately in opposite directions. 



395 PLU 

PLATING, ELECTRO— The process of coveriii.<>- any elec- 
trically conducting* surface with a metal by the aid 
of the electric current. 

PLATING, NTGKEL— Electro-plating- with nickel. 

PLATING, SILVEK— Electro-plating- Avith silver. 

PLOW — The sliding" contacts connected to the motor of 
an electric street car, and placed within the slotted 
underground conduit, and provided for the purpose 
of taking* off the current from the electric mains 
placed therein, as the contacts are pushed forward 
over them by the motion of the car. 

PLUG— A piece of metal in the shape of a plug*, provided 
for making* or breaking* a circuit by placing- in, or re- 
moving* from, a conical opening* formed in the ends 
of two closely approached pieces of metal which are 
connected with the circuits to be made or broken. 

PLUG, SAFETY— A wire, bar, plate or stripe of readily fus- 
ible metal, capable of conducting, without fusing, the 
current ordinarily employed on the circuit, but which 
fuses, and thus breaks the circuit, on the passage of 
an abnormal current. 

PLUG, SHORT-CTIiCUITlNG— A plug by means of which 
one part of a circuit is cut out by being short-cir- 
cuited, 

PLLTi, WALL — A plug provided for the insertion of a 
lamp or other electro-receptive device in a wall soc- 
ket, and thus connecting it with a lead. 

PLUGS, GKIB— Plugs of active material that fill the spaces 
or apertures in the lead grid or plate of a storage bat- 
tery. 



POL 



396 



PLUNGE BATTERY— (See Battery, Plunge.) 

POINT, CAPiBON— A term formerly applied to the car- 
bon electrodes used in the production of the voltaic 
arc. 

POT.N^TS, NEITTRAT. OF DYNAMO-I'LECTPtIC MACHINE 
— Two points of greatesit diflerence of potential, sit- 
L^ated on the commutator cylinder, at the oi^posito 
ends of a diameter thereof, at which the collecting 
brushes must rest in order to carry off the current 
quietly. 



POLAPilTY, IVLVGNETIC— The polarity acquired by* a 
magnotiza 
netic field 



magnetizable substance when brought into a mag- 



POLARIZATIOX— A counter E. M. F. produced by the pas- 
sage of a current through an electric couple or battery. 

P0IAR1Z!:D APMATUPvE— See Armature, Polarized. 

POIiE CHANGER— A switch or key for changing or re- 
versing the direction of current produced by any elec- 
tric source, such as a battery, 

POLE, CONSEQUENT— A magnet pole formed by two free 
north or two free south poles placed together. 

POLE, MAGNETIC, FREE— A poJe in a piece orf iron, or 
other paramagnetic substance, which acts as if it ex- 
isted as one magnetic pole only. 

POLE, MAGNETIC, NORTH— That pole of a magnetic 
needle which points approximately to the earth's geo- 
graphical north. 



39? POL 

POLE, MAGNETIC, NORTH-SEEiaNG-That pole of a 
magnetic needle whieli points apj)roxiniMtely tOAvards 
the eartli's geographical north. 

POLE, MAGNETIC SALIENT— A term sometimes applied 
to the sing'le poles at the extremities of an anomalous 
magnet in order to distinguish them from the double or 
consequent pole formed by the juxaposition of two 
similar magnetic poles. 

POLE, MAGNETIC, SOUTH— That pole of a magnetic 
needle which points approximately towards the earth's 
geographical south. 

The ^outh-seeking pole of a magnetic needle. 

POLE, NEGATIVE -That pole of an electric source 
through which the current is assumed to enter or flow 
back into the source after having passed through the 
circuit external to the source. 

POLE, POSITIVE— That pole of an electric source out of 
which the electric current is assumed to flow. 

POLIJ, TELEGPtAPHIC— A wooden or iron upright on 
which telegrapliic or other wires are hung. 

POLE, TROLLEY— The pole which supports the trolley 
bearing and rests on the socket in the trolley base 
frame in an overhead vn're electric railway system. 

POLES, MAGNETIC— The two points where the lines of 
magnetic force pass from the iron into the air, and 
from the air into the iron. 

The two points in a magnet where the magnetic 
force appears to be concentrated. 



POT 



398 



POPGUN, I:LECTK0-:MAG NETIC— a magnetizing coil, 
provided with a tubular space for The insertion of a 
core, much shorter than the length of the coil, which, 
when the enersri^'ing- current is passed through the 
coil, is thrown violentl}^ out from the coil. 

POFvOUS CUP— (See Cup, Porous.) 

POSITIVE DIRECTION OF LINES 01' MAGNETIC FORCE 
— (See Force, ^Magnetic, Lines of, Positive Direction 
of.) 

POSITIVE PLATE OF STORAGE BATTERY— See Plate, 
Positive, of Stort^ge Battery.) 

POSITIVE PLATE OF VOLTAIC CELL— (See Plate, Posi- 
tive, of Voltaic Cell.) 

POSITIVE POLE— (See Pole, Positive). 

POST, BINDING — A device for connecting the terminal 
of an electric source with the terminal of an electro- 
receptive device, or for connecting different parts of 
an electric apparatus with one another. 

POTENTIAL, ALTERNATING— A potential, the sign of 
direction of which is alternately changing from posi- 
tive to negative. 

POTENTIAL CONSTANT— A potential which remains con- 
stant under all conditions. 

POTENTIAL, DIFFERENCE OF— A term employed to de- 
note that portion of the electromotive force which 
exists between any two points in a circuit. 

POTENTIAL, ELECTRIC— The power of doing electric 
work. 
Electrical level. 



399 POW 

POTElSn^IAL, F\LL OF— A decrease of potential in the 
direction in which an electric current is iiowing-, pro- 
portional to the resistance when the current is con- 
stant. 

POTENTIAL, MAGNETIC— The amonnt of work required 
to bring" ux) a unit north -seeking magnetic pole from 
an iniinite distance to a given point ii: a magrsetic 
field. 

POTENTIAL, UNIT DIFFERENCE OF— Such a diU'erence 
of potential between two points that requires the ex- 
penditure of one erg of work to bring a unit of posi- 
tive electricit}^ from one of these points to another, 
against the electric force. (See Erg.) 

The practical tinit- of difference of potential is the 
volt. 

POTENTIOMETEE-^An apparatus for the galvanometer 
measurement of electromotive forces, or differences of 
potential, by a zero method. 

PO^^ER— Rate of doing work. 

Mechanical power is generally measured in horse 
power, which is equal to work done at the rate of 550 
foot-pounds per second. 

POWER, CANDLE— An intensity of light emitted from a 
luminous body equal to the light produced by a stand- 
ard candle. 

POWER, CANDLE, NOMINAL— A term sometimes applied 
to the candle-power taken in a certain favorable direc- 
tion. 

This term is generally used in arc lighting. In the 
ordinary arc lamp the greatest amount of light is 
emitted at a particular point, viz: from the crater in 
the upper or positive carbon. 



PRI 



400 



POWEE, CANDLE, SPHERICAL— The average or mean 
value of canr'le power taken at a number of points 
arourd the source of light. 

POWEK, CONDUCTING, FOR ELECTRICITY -The ability 
of a given length and area of cross-section of a sub- 
stance to conduct electricity, as compared with an 
equal length and area of cross-section of some other 
substance, such as pure silver or copper. 

POWER, ELECTRIC— Power developed by means of elec- 
tricity. 

POWER, ELECTRIC, DTSTRII5UTI0N OF-The distribu- 
tion of electric power by means of any suitable system 
of generators, connecting circuits and electric motors. 

POWER, ELECTRIC TRANSMISSION OF— The transmis- 
sion of mechanical energy by converting it into elec- 
tric energy at one point or end of a line, and recon- 
verting at some distant point from electrical to me- 
chanical energy. 

POWER, HORSE— A rate of doing work equal to 550 foot- 
pounds per second, or 33,000 foot-pounds per minute. 

POWER, HORSE, ELECTRIC— Such a rate of doing electric 
work as is equal to 746 watts per second. 

This rate is equivalent to 33,000 foot-pounds per min- 
ute, or 550 foot-pounds per second. 

POWER, PROJECTING, OF MAGNET— The power a mag- 
net possesses of throwing or projecting its lines of 
magnetic force across an intervening air space or gap. 

PRESSURE W^TRES— (See Wires, Pressure). 
PRIMARY COIL— (See Coil, Primary). 



401 QUA 

PRIMAKY, THE — That conductor in an induction coil, or 
transformer, v/hich receives the impressed electromo- 
tive force, or which carries the inducing current. 

PRIME CONDUCTOR— (See Conductor Prime). 

PRONY BRAKE— (See Brake, Prony). 

PULL, EliECTRlC BELL —A circuit-closing device operated 
by a pull. 

PULSATING CURRENT— (See Current, Pulsating). 

PUMP, AIR, MERCinilAL— A device for obtaining a high 
vacuum by the use of mercury. 

PUMP, AIR, SPRENGEL'S MERCURIAL— A mercurial air 
pump in which the vacuum is obtained by means of the 
fall of a stream of mercury. 

PUSH — A name sometimes applied to a push button, or to 
a floor push. 

PUSH BUTTON— (See Button, Push). 

PYRO-ELECTRICITY— (See Electricity, Pyro). 

PYROMETER, SIEMEN'S ELECTRIC— An apparatus for 
the determination of temperature by the measurement 
of the electric resistance of a platinum wire exposed 
to the heat whose temperature is to be measured. 



QUADRATURE, IN — A term employed to express the fact 
that one simple periodic quantity lags 90 degrees be- 
hind another. 

QUANTITY, UNIT OF ELECTRIC— A definite amount or 
quantity of electricity called the coulomb. 



RAI 



402 



K — A coij traction used for ohmic resistance. 

RADIATION, ELECTEO-MAGNETIC— The sending ou in 
all directions from a conductor, through which an os- 
cillating discharge is passing, of electro-magnetic waves 
in all respects similar to those of light except that they 
are of much greater length. 

RAILROAD, ELECTRIC— A railroad, or railway, the cars 
on which are driven or propelled by means of electric 
motors connected with the cars. 

RAILROADS, AUTOMATIC ELECTRIC SAFETY SYSTEM 
FOR — A system for automatically preventing the ap- 
proach of two trains at an^^ speed beyond a predeter- 
ing safety from collisions of moving railroad trains by 
dividing the road into a number of blocks or sections 
of a given length, and so maintaining telegraphic com- 
munication between towers located at the ends of each 
of such blocks as to prevent, by the display of suitable 
signals, more than one train or engine from being on 
the same block at the same time. 



RAILROADS, ELECTRIC, CO^'TINUOUS OVERHEAD 
SYSTEM OF MOTIVE POWER FOR— A variety of the 
dependent system of motive power for electric railroads 
in which a continuous bare conductor is connected with 
the terminals of a generating dynamo, and supported 
overhead by suitable means, and a traveling wheel or 
trolley is moved over the same by the motion of the 
ear, in order to carry off the current from the line to 
the car motor. 



403 BAI 

RATLROADS, ELECTRIC, CONTINUOUS SURFACE SYS- 
TEM OF MOTIVE POWER FOR— A variety of the de- 
pendent system of motive power for electric railroads, 
in w^liicli the terminals .of the generating* dynamo are 
connected to the continuous bare metallic conductor 
that extends along- the entire track on the s^irface of 
the roadway or street, and from which the current is 
taken off by means of a traveling conductor connected 
with the moving car. 

RAILROADS, ELECTRIC, CONTINUOUS UNDERGROUND 
SYSTEM OF MOTIVE POWER FOR— A variety of the 
dependent system of motive power for electric rail- 
ways, in which a continuous bare conductor is placed 
underground in an open slotted conduit, and the cur- 
rent taken otf from the same by means of sliding or 
rolling contacts carried on the moving car. 

RAILROADS, ELECTRIC, DOUBLE-TROLLEY SYSTEM 
FOR — A system of electric railroad propulsion, in which 
a double trolley is employed to take the driving cur- 
rent from two overhead trolley \vires. 

RAILROADS, ELECTRIC, INDEPENDENT SYSTEM OF 
MOTIVE POWER FOR— A term for the electric pro- 
pulsion of railway cars by means of primary or storage 
batteries placed on the car and directly connected with 
the motor, 

RAILROADS, ELECTRIC, SINGLE-TROLLEY SYSTEM— 
A system of electric railroad propulsion in which a 
single trolley is employed to take the driving current 
from a single overhead trolley wire. 



REC 



404 



RAY, EI<ECTRIC— A species of fish named the ray, which, 
like the electric eel, possesses the power of prod 
electricity. 



ucing 



RECEIVER, HARMONIC— A receiver, employed in systems 
of harmonic teleg-raphy. consisting of an electro-mag- 
netic reed, tuned to vibrate to one note or rate only. 

RECEIVER, PHONOGRAPHIC— The apparatus employed 
in a telephone, phonograph, graphophone or gramo- 
phone for the reproduction of articulate sj)eech. 

RECEIVER, TELEPHONIC— The receiver employed in the 
telephone. 

RECORD, GRAMOPHONE— The irregular indentations, cut- 
lings or tracings marie by a point attached to the dia- 
phragm spoken against, and employed in connection 
with the receiving diaphragm for the reproduction of 
articulate speech. 

RECORDER, CHEMICAL, BAIN'S— An apparatus for re- 
cording the dots and dashes of a ^lorse telegraphic dis- 
patch, on a sheet of chemically prepared paper. 

RECORDER, MORSE- An apparatus for automatically re- 
cording the dots and dashes of a Morse telegraphic dis- 
I)atch. on a fillet of paper drawn under an ijidenting 
or marking point on a striking lever, connected with 
the armature of an electro-magnet. 

RECORDER, SIPHON— An apparatus for recording in ink 
on a sheet of paper, by means of a fine glass siphon 
supported on a fine wire, the message received over a 
cable. 

RECTIFIED— -Turned in one and ** same direction. 



405 REL 

REFLECTING GALVANOMETER— (See Galvanometer, Re- 
flecting). 

REGISTER, TELEGRAPHIC— An apparatus employed at 
the receiving" end of a telegraphic line for the purpose 
of obtaining^ a permanent record of the telegraphic 
dispatch. 

REGISTER, WATCHMAN'S ELECTRIC— A device for per- 
manently recording the time of a watchman's visit to 
each of the different localities he is required to visit at 
stated intervals. 

REGULATION, AUTOMATIC, OP DYNAMO-ELECTIvJC 
MACHINE — Such a regulation of a dynamo eiectric 
machine as will automatiealU present constant either 
the current or the potential difference. 

REGULATION, HAND— Such a regulation of a dynamo- 
electric machine as will preserve constant, either the 
current or the potential, said regulation being etfected 
by hand as distinguished from automatic regulation. 

REGULATOR, AUTOMATIC— A device for securing auto- 
matic regulation as distinguished fromhand regulation. 

RELAY^An electro-magnet, employed in systems of tel- 
egraphy, provided with contact points placed on a deli- 
cately supported armature, Ihe movements of which 
throw a battery, called the local battery, into or out 
of the circuit of the receiving apparatus. 

RELAY, DIFFERENTIAL— A telegraphic relay containing 
two differentially wound coils of wire on its magnet 
cores. 

RELAY MAGNET — A name ::ometimes given to a relay. 



RES 



406 



RELAY, MICROPHONE— A devnce foi- autoinatleally repeat- 
ing a telephonic message over another wire. 

RELAY, POLARIZED -A telegraphic relay provided with a 
permanently magnetized armature in place of ihe soft 
iron armature of the. ordinary instrument. 

RELUCTANCE, MAGNETIC--A term recently proposed in 
place of magnetic resistance to express the resistance 
offered by a medium to the passage through its mass 
of lines of magnetic force. 

RELUCTANCE, MAGNETIC, UNIT OF- -Such a magnetic 
reluctance in a closed circuit that permits unit mag- 
netic flux to traverse it under the action of unit mag- 
neto-motive force. 

REPEATERS, TELEGRAPHIC --Telegraphic devices v. here- 
by the rela3% sounder or i*egioteriug apparatus, on the 
opening and closing of another circuit, wUh which it is 
suitably connected, is caused to repeat the signals re- 
ceived. 

REPULSION, ELECTRO-DYNAMIC— The mutual repulsion 
between two electric circuits whose currents are floAV- 
ing in opposite directions. 

REPULSION, ELECTRO-MAGNETFC— The mr.tual repul- 
sion produced by two similar electromagnetic poles. 

REPULSION, ELECTROSTATIC- -The mutual repulsion 
produced by tw^o similar electric charges. 

REPULSION, MAGNETIC~The mutual repulsion exerted 
between two similar magnetic poles. 

RESIDUAL MAGNETISM— (See Magnetism, Residual). 



40? RE9 

RESIN — A g-eneral term applied to a /aviety of dried juices 
of vegetable orig-in. 

RESISTANCE— Something- placed in a oircirit for the pur- 
pose of opposing the passage or f.ovv of the current in 
the circuit or branches of the circuit in which it ,is 
placed. 

The electrical resistance of a conductor is that quality 
of the conductor in virtue of which there is a fixed nu- 
merical ratio between the potential dift'erence of the 
two opposing faces of a cubic unit of such conductor, 
and the quality of electricity which traverses either 
face per second, assuming a steady flow to take place 
normal to these faces, and to be uniformly distributed 
over them, such flow taking place solely by an electro- 
motive force outside the volume considered. 

RESISTANCE, ABSOLUTE UNIT OF— The one thousand 
millionth of an ohm. 

RESISTANCE POX— (See Box, Resistance). 

RESISTANCE COIL— (See Coil, Resistance). 

RESISTANCE, EFFECT OF HEAT ON ELECTRIC— Nearly 
ail metallic conductors have their electric resistance 
increased by an increase of temperature. 

The carbon conductor of an incandescent electric 
lamp, on the contrary, has its resistance decreased 
when raised to electric incandecsence. The decrease 
amounts to about three-eighths of its resistance when 
cold. 

RESISTANCE, ELECTRIC— The ratio between the electro- 
motive force of a circuit and the current that passes 
therein. The reciprocal of electrical conductivity. 



L 



RES 408 

RESISTANCE, ELECTRIC, OF LIQUIDS— The resistance 
offered bv a liquid mass to the passage of an electric 
current. 

As a rule the electric resistances of liquids, with the 
single exception of mercury, are enormously higher 
than those of metallic bodies. 

RESISTANCE, FALSE— A resistance arising from a coun- 
ter electromotive force, and not directly from the di- 
mensions of the circuit, or from its specific resistance. 

RESISTANCE, INDUCTIVE— A resistance which possesses 
self-induction. 

RESISTANCE, 'insulation— The resistance of a line or 
conductor existing between the line or conductor and 
the earth through the insulators, or between the two 
wires of a cable through the insulating material sepa- 
rating them. 

RESISTANCE, MAGNETIC— The reciprocal of magnetic 
permeabilitj'- or conductibility for lines of magnetic 
force. Resistance otTered by a medium to the passage 
of the lines of magnetic force through it. 

RESISTANCE, NON-INDUCTIVE— A resistance in which 
self-induction is practically absent. 

RESISTANCE, OHMIC— The true resistance of a conductor 
due to its dimensions and specific conducting power, as 
distinguished from the spurious resistance produced 
by a counter electromotive force. 

RESISTANCE, OR CELL, SELENIUM— A mass of crystal- 
line selenium, the resistance of which is reOuced by 
placing it in the form of narrow strips between the 
edges of broad conducting plates of brass. 



409 RHB 

RESIST AN^CE, SECONDARY— A ierm sometimes used in 
place of external secondary resistance. 

RESISTANCE, SPECIFIC— ^fhe particular resistance which 
a substance oifers to the passag-e of electricity throug'h 
it. 

RESISTANCE, UNIT OF— Such a resistance that unit dif- 
ference of potential is required to cause a current of 
unit strength to pass. (See Ohm). 

RESONANCE, ELECTRIC— The setting up of electric pulses' 
in open-circnited conductors, by the action of pulses in 
neighboring conductors. 

RESONATOR, ELECTRIC— An apparatus employed by 
Hertz in his investigations on electric resonance. 

RESULTANT ---In mechanics, a single force that represents 
in direction and intensity the effects of two or more 
separate forces. 

RETARDATION— A decrease in the speed of telegraphic 
signaling caused either by the induction of the line 
conductor on itself, or by mutual induction between it 
and neighboring conductors, or by condenser action, 
or by all. 

REVERSIBILITY OF DYNAMO— The ability of a dynamo 
to operate as a motor when traversed by an electric 
current. 

REVERSING KEY— (See Key, Reversing). 

RHEOSTAT— An adjustable resistance. 

A rheostat enables the current to be brought to a 
standard, i. e,, to a fixed value, by adjusting the resist- 
ance; hence the name. 



RUE 



410 



KHEOSTAT, WATER— A rheostat the resistance of which 
is obtained by means of a mass of water of fixed di- 
mensions. 

RING PACIXNOTTI— A kind of grame ring- containing 
spaces or grooves for wire bobbins formed in the iron 
of the ring. 

ROCKER, BRUSH — Tn a dynamo-electric machine or elec- 
tric motor, any device for shifting the position of the 
brushes on the commutator cylinder. 

ROD, CLUTCH — A clrtch or clamp provided in an arc lamp 
to seize the lamp rod and thus arrest its fall, during 
feeding, beyond a certain point. 

ROD, LAMP — A metallic rod provided in electric arc lamps 
for holding the carbon electrodes. 

ROD, LIGHTNING— A rod, or wire cable of good conduct- 
ing material, placed on the outside of a house or other 
structure, in order to protect it from the effects of a 
lightning discharge. 

ROD, LIGHTNING, POINTS ON— Points of inoxidizable 
material, placed on lightning rods, to effect the quiet 
discharge of a cloud by convection streams. 

ROSETTE — An ornamental plate provided with contacts 
connected to the terminals of the service wires, and 
placed in a wall for the readj^ attachment of the i,n- 
candescent lamp. 
A word sometimes used in place of rose. 

ROTARY-PHASE CURRENT— (See Cui-rent, Rotating). 

ROTATING CURRENT— (See Current, Rotating). 

RUHMKORFF COII^(See Coil, Rhumkorff). 



411 SEC 

s 

S. — A contraction employed for second. 

SATURATION, :^^AG^'^ETIC— The maximnm mag'netization 
which can be imparted to a maefnetic substance. 

The condition of iron, or other paramagTietic sub- 
stance, when its intensity of mai>-neti7ation is so g-reat 
that it fails to be further sensibly magnetized by any 
magnetic force, however great. 

SCALE, THERMOMETEK, CENTIGRADE— A thermometer 
scale, in which the length of the thermometric tube 
between the melting point of ice and the boiling point 
of water is divided into one hundred equal parts or 
degrees. 

SCALE, THERMOMETER, FAHRENHEIT'S— A thermom- 
eter scale in which the length of the thermometer tube 
between the melting point of ice and the boiling point 
of water is divided into 180 equal parts called degrees. 

SCREEN, Mx\GNETIC— A hollow box whose sides are made 
of thick iron, placed around a magnet or other body 
so as to cut it oft* or screen it from any magnetic field 
external to the box. 

SCREENING, MAGNETIC— Preventing magnetic induction 
from taking place by interposing a metallic plate, or a 
closed circuit of insulated wire, between the body pro- 
ducing the magnetic field and the body to be mag- 
netically screened. 

SECOND, WATT— A unit of electrical work. 

SECONDARY BATTERY— (See Battery, Secondary). 



SER 



412 



SECOXDAEY COIL— (See Coil, Secondary). 

SECONDARY, MOVABLE— The secondary condactor of an 
induction coil, which, instead of being fixed as in most 
coils, is movaV)le. 

SECTION, TROLLEY- A sing-le continuous length of trol- 
ley wire, with or without its branches. 

SEISMOGRAPH, MICRO— An electric apparatus for photo- 
crraphically registering* the vibrations of the earth pro- 
duced by earthquakes or other causes. 

SELENIUM — A comparatively rare element generally found 
associated with sulphur. 

SELENIUM CELL— (See Cell, Selenium). 

SELF-INDUCTION— (See Induction, Self). 

SEMAPHORE — A variety of signal apparatus employed In 
railroad block systems. 

SEPARATOR — An insulating sheet of ebonite, or other 
similar substance, corrugated and perforated so as to 
conform to the outline of the plates of a storage bat- 
tery, and placed between them at suitable intervals, in 
such a manner as to avoid short-circuiting, without 
impeding the free circulation of the liquid. 

SERIES, CONTACT— A series of metals arranged in such 
an order that each becomes positively electrified by 
contact with the one that follows it. 

SERIES DISTRIBUTION OF ELECTRICITY BY CON- 
STANT CURRENTS— (See Electricity, Series Distribu- 
tion of, by Constant Current Circuit). 



413 SHU 

SERIES, THERMO-ELECTRIC— A list of metals so arrang- 
ed according" to their thermo-electric powers, that each 
metal in the series is electro-positive to any metal 
lower in the list. 

SERIES TURNS OF DYNAMO-ELECTRIC MACHINE— (See 
Tnrns, Series, of Dynamo-Electric Machine). 

SERIES WINDING- (See Winding, Series). 

SERIES-WOUND DYNAMO— (See Dynamo, Series). I 

SHELLAC — A resinous substance possessing valuable insu- 
lating properties, which is exuded from the roots and 
branches of certain tropical plants. 

SHOCK, ELECTRIC— The physiological shock produced in 
an animal by an electric discharge. 

SHORT-CIRCUIT— To establish a short circuit. 

SnU^T — An additional path established for the passage 
of an electric current or discharge. 

SHUNT — To establish an additional path for the passage 
of an electric current or discharge. 

SHUNT CIRCUIT— (See Circuit, Shunt). 

SHUNT DYNAMO-ELECTRIC MACHINE— (See Machine, 
Dynamo-Electric, Shunt-Wound). ' 

SHUNT, GALVANOMETER— A shunt placed around a sen- 
sitive galvanometer for the purpose of protecting it 
from the effects of a strong current, or for altering its 
sensisbility. 

SHUNT, MAGNETIC— An additional path of magnetic ma- 
terial provided in a magnetic circuit for the passage of 
the lines of force. 



SPA 414 

SHUTTLF ARMATURE— (See Armature, Shitttle.) 

SILVER PLATING— (See Plating, Silver.) 

SIPHON, ELKCl RIC— A siphon in which the stoppage of 
flow, due to the gradual accumulation of air, is pre- 
vented by electrical means. 

SMELTIISG, ELECTRO— The separation or reduction of 
metallic substances from their ores by means of electric 
currents. 

SNAP SWITCH— (See Switch, Snap.) 

SOCKET, ELECTRIC LAMP— A support for the reception 
of an incandescent electric lamp. 

SOCKET, WALL — A socket placed in a w^all and provided 
with openings for the insertion of a wall plug w^ith 
w^hich the ends of a flexible twin-lead are connected. 

SOLENOID — A cyclindrical coil of wire the convolutions of 
which are circular. 

An electro-magnetic helix. 

SOLENOID CORE— The core, usually of soft iron, placed 
within a solenoid and magnetized by the magnetic field 
of the current passing through the solenoid. 

SOLUTION, BATTERY— The exciting liquid for voltaic 
cells. (See Cell, Voltaic.) 

SOURCE, ELECTRIC~Any arrangement capable of main- 
taining a difl'erence of potential or an electromotive 
force. 

SPARK COIL- (See Coil, Spark.) 
SPARK, GAI»-(See Gap, Spark.) 



415 ST A 

SPARKING, LINE OF LEAST— The line on a commutator 
cylinder of a dynamo connecting the points of contact 
of the collecting brushes where the sparking is a mini- 
mum. 

SPARKING OF DYNAMO-ELECTRIC MACHINE— (See Ma 
chine, Dynamo-Electric, Sparking of.) 

SPECIFIC INDUCTIVE CAPACITY— (See Capacity, Speci- 
fic. 

SPHERICAL ARMATURE— (See Armature, Spherical.) 

SPIDER, ARMATURE- -A light framework or skeleton 
consisting of a central sleeve or hub keyed to the arma- 
ture shaft, and provided with a number of radial 
spokes or arms for fixing or holding the armature core 
to the dynamo-electric machine. 

SPRING- JACK — A device for readily inserting a loop in a 
main electric circuit. The spring-jack is generally 
used in connection with a multiple switch board. 

STAGGERIXG — A term sometimes applied to the position 
of the brushes on a commutator cylinder, in which one 
brush is placed slighth^ in advance of the other brush 
so as to bridge over a break. 

STANDARD, DYNAIMO- The supports for the bearings of 
a dynamo-electric machine. 

STATION, CENTRAL— A station, centrally located, from 
which electricity for light or power is distributed by a 
series of conductors radiating therefrom. 

STATION, TRANSFORMING— In a system of distribution 
by transformers or converters a station where a number 
of transformers are placed, in order to supply a group 
of houses in the neighborhood. 



/ 



sus 



416 



STOOL, INSULATING— A support isolated from the ground 
usually by glass insulators. 

STORAGE BATTKKY— (See Battery, Storage.) 

STORAGE CELL— (See Cell, Storage.) 

STORM, ELECTRIC— An unusual condition of the atmos- 
phere as regards the quantity of its free electricity. 

STOR^r, MAGNETIC— Irregularities occurring in the dis- 
tribution of the earth's magnetism, affecting the mag- 
netic declination, dip, and intensity. 

STRENGTH, FIELD— The intensity or total flux of magn- 
etism of a dynamo. 

STRIPPING — Dissolving the metal coating from a silver- 
X)lated or other metal-plated article. 

SUBMARINE CABLE— (See Cable, Submarine.) 

SUBWAY, ELECTRIC— An accessible underground way or 
passage provided for the reception of electric wires or 
cables. 

SULPHATING--A name applied to one of the sources of 
loss in the operation of a storage battery, by means 
of the formation of a coating of inert sulphate of Jead 
on the battery plates. 

SL^SCEPTIBILITY, MAGNETIC- The ratio existing be- 
tween the induced magnetization and the magnetic 
force producing such magnetism, or the intensity of 
magnetism divided by the magnetic force. 

SUSPENSrON, BTFILAR— The suspension of a needle by 
iwo parallel wires or fibres, as distinguished from a 
suspension by a single wire or fibre. 



41? SWI 

SUSPENSION, KNIFE-EDGE— The suspension of a needle 
on knife edg-es that are supported on steel or agate 
planes. 

SWITCH BOAKD- (See Board, Switch.) 

SWITCH, BPiEAK-])OWN— A special switch, employed in 
small three-wire systems, for connecting the positive 
and negative bus-wires in such a manner as to prac- 
tically convert it into a two-wire system and permit 
the system to be supplied with* current from a single 
dynamo. 

SWITCH, CHANGING— A switch designed to throw a cir- 
cuit from one electric source to another. 

SWITCH, J)OUBLE-BREAK KNIFE— A knife switch pro- 
vided with double-break contacts. 

SWITCH, DOUBLI'-POLE— A switch that makes or breaks 
contact with both poles of the circuit in which it is 
placed. 

A switch consistinsr of a combination of two separate 

C3 J. 

switches, one connected to the positive lead and the 
other to the negative lead. 

SWITCH, I'ii]EDFPv— The switch employed for connecting 
or disconnecting each conductor of a feeder from the 
bus-bars in a central station. 

SWITCH, TfNIFE--A switch which is opened or closed by 
the motion of a knife contact which moves between 
parallel contact plates. 
A knife-edge switch. 

SWITCH, PifiVEHSING— A switch for reversing the direc- 
tion ot a circuit. 



TAG 



418 



bnVlTCH, SNAP— A switch in which the transfer of the 
contact points from one position to another is accom- 
plished b3^ means of a quick motion obtained by the 
operation of a spring. 

.^' WITCH, TELEPHONE, AUTOMATIC— A device for auto- 
matically transferring" the connection of the main line 
from the call bell to the telei)hone circuit. 

SWITCH, THEEE-POINT— A switch by means of which 
a circuit can be completed through three different con- 
tact points, 

SWITCH, TIME— An automatic switch in which a prede- 
termined time is required either to insert a resistance 
in or remove it from a circuit. 

SWITCH, TWO-POINT— A switch by means of wliich 
a circuit can be completed through two different 
contact points. 

SYSTE:Nr, THREE-WIEE— A system of electric distribution 
for lartjps or other translating devices connected in 
multiple, in which three wires are used instead of the 
two usually emplo^^ed. 

In the three-wire system two dynamos are generally 
employed, w^hich are connected with one another in 
series. 



T. — A symbol used for time. 

T.'VCHOMETER — An apparatus for indicating at any mo- 
ment on a revolving dial the exact number of revolu- 
tions per minute of a shaft or machine. 



419 TEL 

1 ALK, CROSS — In telephony an indistinctness in the 
speech transmitted over any circuit, due to this circuit 
receiving", either by accidental contacts or by induction, 
the speech transmitted over neighboring circuits. 

TANNING, ELECTRIC— An application of electric currents 
to tanning leather. 

'J^APE, INSULATING— A ribbon of flexible material im- 
pregnated with kerite, okonite, rubber or other suitable 
insulating material, employed for insulating wires or 
electri2 condiictors at joints, or other exposed places. 

1\\STE, GALVANIC— A sensation of taste produced when 
a voltaic current is passed through the tongue or in the 
neighborhood of the gustatory nerves, or nerves of 

TEASER, ELECTRIC CURRENT— A coil of fine wire placed 
on the field magnets of a dynamo-electric machine, 
next to the series coil wound thereon, and connected 
as a shunt across the main circuit. 

This term is also used to designate the auxiliary 
winding used for producing the polyphase current in 
a monocyclic dynamo. 

TECHNICS, ELECTRO— The science which treats of the 
physicnl applications of electricity and the general 
principles applying thereto. 

TELEGRAPHIC— Pertaining to telegraphy. 
TELEGRAPHIC ALPHABET— (See Alphabet, Telegraphic.) 
TELEGRAPHIC CABLE— (See Table, TelegrapTiic.) 
TELEGRAPHIC CODE— (See Code, Telegraphic.) 



.// 



TEL 



420 



TELEGKAPHIC KEY— (See Key, Telegraphic.) 

TELEGEAPHING — Sending- a communication by means of 
telegraphy 

TELEGEAPHY, ACOUSTIC— A non-recording system of 
telegraphic commnnlcation, in which the dots and 
dashes of the Morse system, or the deflections of the 
needle in the needle systems, are replaced by sounds 
that follow one another at intervals, that represent 
the dots and dashes, or the deflections of the needle, 
and thereby the letters of the alphabet. 

TELEGRAPHY AND TELEPHONY, SIMULTANEOUS, 
0\ EK A SINGLE WIRE— Any system for simultaneous 
transmission of telegraphic and telephonic messages' 
over a single wire. 

'I'ELEGEAPHY, AUTOMATIC— A system by means of 
which a telegraphic message is automatically trans- 
mitted by the motion of a pre^^ousl3' perforated fillet 
of paper containing perforations of the shape and order 
required to form the message to be transmitted. 

TELEGRAPHY, CHEMICAL— A system by means of which 
the closings of the mainline-circuit, corresponding to 
the dots and dashes of the Morse alphabet, are recorded 
on a fillet of paper by the electroJytic action of the cur- 
rent on a chemical substance \^ith which the paper 
fillet is impregnated. 

TELEGRAPHY, DIPLEX— A method of simultaneously 
sending two messages in the same direction over a sin- 
gle wire. 

Diplex telegraphy is to be distinguished from duplex 
telegraphy, where two messages are simultaneously 
transmitted over a single wire in opposite directions, 



421 



TEL 



TELEGEAPHY, DUPLEX, BRIDGE METHOD OF— A sys- 
tem whereby two telegraphic messages can be simul- 
taneously transmitted over a single wire in opposite 
directions. 

TELEGPvAPHY, DUPLEX, DTFFE"REXTIAL METHOD OF 
— A system of duplex telegraphy in which the coils of 
the receiving and transmitting instruments are differ- 
entially wound. 

TELEGRAPHY, FAC-SIMILE— A system whereby a fac- 
simile or copy of a chart, diagram, picture or signature 
is telegraphically transmitted from one station to 
another. 

TELI^IGRAPHY, FIRE ALAR.^— A system of telegraphy 
by means of which alarms can be sent to a central sta- 
tion, or to the fire engine houses in the district, from 
call boxes placed on the line. 

TELEGRAPHY, GRAY'S HARMONIC MULTIPLE-A sys- 
tem for the simultaneous transmission of a number of 
separate and distinct musical notes over a single wire, 
which separate tones are utilized for the simultaneous 
transmission of an equal number of telegraphic mes- 



TELEGRAPHY, IINDUCTIOX-A system of telegraphing 
by induction between moving trains and fixed stations 
on a railroad, by means of impulses transmitted by in- 
duction between the car and a wire parallel with the 
track. 

TELEGRAPHY, INDUCTION, CURRENT SYSTEM OF--A 
system of induction telegraphj^ depending on current 
induction between a fixed circuit along the road, and a 
parallel circiiit on the moving* train. 



■.^/^ 



TEL 



422 



TELEGRAPHY, INDUCTIOIV, STATIC SYSTEM OF— A 
system of inductive telegraphy depending- on the static 
induction between the sending and receiving- instru- 
ment. 



TELEGRAPHY, MORSE SYSTEM OF— A system of tele- 
graphy in which makes and breaks occurring ar inter- 
vals corresponding to the dots and dashes of the Morse 
alphabet are received by an electro-magnetic sounder 
or receiver. 

TELEGRAPHY, :N[ULTIPLEX— A system of telegraphy for 
the si n:\iiltaneous transmission of inore than four sepa- 
rate messages over a single wire. • 

TELEGRAPHY, PRINTING- A system of telegraphy in 
which the messages received are ^Drinted on a paper fil- 
let. 

TELEGRAPHY, QUADRUPLEX— A system for the simul- 
taneous transmission of four messages over a single 
Avire, two in one direction and the remaining two in 
the opposite direction. 

TELEGRAPHY, QUADRUPLEX, BRIDGE METHOD OF— 
A system of quadruplex telegraphy by means of a 
double bridge duplex sj^stem. 

TELEGRAPHY, QUADRUPLEX, DIFFERENTIAL ^fETH- 
OD OF — A system of quadruplex telegraphy by means 
of a double ditTerential duplex system. 

TELEGRAPHY; SIMPLEX— A system of telegraphy iu 
which in a single message only can be sent over the 
line. 



423 THE 

TELEGRAI^HY, STEP-BY-STEP— A system of telegraphy 
in which the signals are registered by the nio^ ernents 
of a needle over a dial on which the letters of the al- 
phabet, etc., are marked. 

TELEGRAPHY, SUBMARINE— A system of telegraphy in 
which the line wire consists of a submarine cable. 

TELEGRAPHY, SYNCHRONOUS-MUIiTIPLEX, DELANY'S 
SYSTEM— A system devised b}^ Delany for the simul- 
taneous telegraphic transmission of a number of mes- 
sages either all in the same direction, or part in one 
direction and the remainder in the opposite direction. 

TELEGRAPHY, WRITING— A species of fac-simile tele- 
graphy, by means of which the motions of a pen at- 
tached to a transmitting instriiment so vary the resis- 
tance on two lines connected with a receiving instru- 
ment as to cause the current received thereby to re- 
produce the motions, on a pen or stylus, which trans- 
fers them to a sheet of paper. 

A sytem of wrriting telegraphy consists essentially of 
transmitting and receiving instruments connected by a 
double line wire. 

TELEPHONE — An apparatus for the electric transmission 
of articulate speech. 

TELEPHONIC EXCHANGE— (See Exchange. Telephonic, 

System of). 
TER^riNALS — A name sometimes ay)plied to the jDoles of a 

battery or other electric source, or to the ends of the 

conductors or wires connected thereto. 
THERAPEUTICS, ELECTRO, OR ELECTRO-THERAPY— 

The application of electricity to the curing of disease. 



/■' 



TOU 



424 



THEKMO-ELECTRIC BATTERY— (See Battery, Thermo- 
Electric.) 

THERMO-ELECTRIC COLELE- (See Couple, Thermo-Elee- 
trio.) 

TTlER:srO!NrETER, ELECTRIC RESISTANCE— A thermo- 
meter the action of which is based on the change in 
the electric resistance of metallic substances with 
changes in temperature. 

TEER0:N[STAT— An instrument for automatically miaintain- 
ing a given tempei;ature by the closing of an electric 
circuit through the expansion of a solid or liquid. 

THERMOSTAT, MERCURIAL- -A thermostat operating by 
the expansion of a mercury column. 

THREE-WIRE SYSTEM— (See System, Three-Wire.) 

TICKER SERVICE, STOCK- -The simultaneous transmis- 
sion of stock quotations or other desired information 
to a number of subscribers. 

TIPS, POLAR— The free ends of the field magnet pole 
pieces of a dj^namo-electric machine. 

TORQUE — That moment of the force applied to a dynamo 
or other machine which turns it or causes its rotation. 
The mechanical rotary or turning force which acts 
on the armature of a dynamo-electric machine or mo- 
tor and causes it to rotate. 

TOUCH, DOUBLE— A method of magnetization in which 
two closely approximated magnet poles are simultane- 
ously dra^vn from one end of the bar to be magnetized 
to the other and back again, and this repeated a num- 
ber of times. 



425 TRA 

TRACTION, MAGNETIC— The force with which a magnet 
holds on to or retains its armature, w^hen once attached 
thereto. 

TRAMWAY, ELT^X'TRIC— A railway over which cars are 
driven by means of electricity. 
An electric railroad. 

TRANSFORMER— An inverted Rnhmkorff induction coil 
employed in systems of distribution by means of al- 
ternating* currents. 

An apparatus for raisdng or lowering the voltage of 
an electric current used in (transmitting and distribut- 
ing power. 

A transformer is sometimes called a converter. The 
word transformer is, however, the one most employed. 

TRANSFORMER, CLOSED IRON CIRCUIT— A transformer 
the core of which forms a complete magnetic circuit. 

These transformers are sometimes called ironclad 
transformers. 

TRANSFORMER, CONSTANT-CURRENT— A transformer 
in which a current of a constant potential in the pri- 
mary is converted into a current of constant strength 
in the secondary, despite changes in the load on the 
secondary. 

TRANSI'ORMER, CORE— A transformer in which the pri- 
mary and secondary wires are wrapped around the out- 
side of a core consisting of a bundle of soft iron wires 
or plates. 

TRANSFORMER, EFFICIENCY OF— The ratio between the 
whole energy supplied in any given time to the pri- 
mary circuit of a transformer and that which appears 
in the form of electric current in the secondary circuit. 

TRANSFORMER, HEDGEHOG— A name applied to a par- 
ticular form of open-iron circuit transformer. 



/ 



TEA 



426 



TRANSFOEMEE, MULTIPLE— Any form Of transformer 
which is connected in multiple to the primary circuit. 

TRANSFOEMEE, OIL--A transformer which is immersed 
in oil in order to insure a high insulation. 

TEAISTSFOEMEE, EOTAEY-CUEEENT-A transformer 
operated by means of a rotary cun^ent. 

TANSFOEMEE, STIELI.— A transformer in which the pri- 
mary and secondary coils are laid on each other, and 
the iron core is then wound through and over them so 
as to enclose all the copper of the primary and sec- 
ondary circuits within the iron. 

TEANSFOEMEE, STEE-DOWN— A transformer in which a 
small current of comparatively great difference of po- 
tential is converted into a large current of comparative- 
ly small difference of potential. 

TEANSFOEMEE, WELDING— A transformer suitable for 
changing a small electric current of comparatively high 
difference of potential, into the heavy currents of low 
difference of potential required for welding purposes. 
Welding transformers have in general a very low re- 
sistance in their secondary coils, and almost invariably 
consist of a single turn or at the most of a few turns 
of very stout wire. 
TEANSLATING DEVICE— (See Device, Translating.) 
TEANSMITTEE, CAEBON, FOE TELEPHONES— A tele- 
phone transmitter consisting of a button of compressi- 
ble carbon. 

The sound waves impart to-and-fro movements to the 
transmitting diaphragm, and this to the carbon but^ 
ton, thus varying its resistance by pressure. This but- 
ton is placed in circuit with the battery and induction 
coil. 



427 • TUR 

TEANSMITTEK, ELECTRIC— A name applied to varioiia 
electric apparatus employed in telegraphy or telephony 
to transmit or send the electric impulses over a line 
wire or conductor. 

TREATMENT, HYDRO-CARBON, OF CARBONS— Exposing 
carbons, while electrically heated to incandescence, to 
the action of a carbonizing gas, vapor or liquid, for the 
purpose of rendering them more uniformly electrically 
conducting throughout. 

TRIMMING — A term sometimes applied to the act of plac- 
ing the carbons in an electric arc lamp. 

TROLLEY — A rolling contact wheel that moves over the 
overhead lines pro\ided for a line of electric railway 
cars, and carries ofE the current required to drive the 
motor car. 

TROLLEY, DOUBLE— The traveling conductors, which 
move more over the lines of wire in any system of 
electric railways that employs two overhead conduc- 
tors. 

TROLLEY POLE— (See Pole, Trolley). 

TUBE, CROOKES --A tube containing a high vacuum and 
adapted for showing any of the phenomena of the 
ultra-gaseous state of matter. 

TUBES, VACUUlSr -Glass tubes, from which the air has 
been partially exhausted and through which electric 
discharges are passed for the production of luminous 
effects. 

TURN, AMPERE — A single turn or winding in a coil of 
wire through which one ampere passes. 



CNI 



428 



TURNS, SERIES, OF DYNAMO-ELECTKTC MACHINES— 
The ampere-turns in the series circuit of a compound- 
wound dynamo-electric machine. 

TURNS, SHUNT, OF DYNAMO-ELECTRIC MACHINE— 
The ampere-turns in the skunt circuit of a compound- 
wound dynamo-electric machiiie. 



u 



UNITS, ABSOLUTE— A system of units based on the centi- 
metre for the unit of length, the g-ramme for the unit 
of mass, and the second for the unit of time. 

UNITS, CENTIMETRE-GRAMME-SECOND— A system ot 
units in which the centimetre is adopted for the unit 
of length, the gramme for the unit of mass, and the 
second for unit of time. 

UNITS, C. G. S. — The centimetre-gramme-seeond units. 

UxVITS, FUNDAMENTAL— The units of length, time and 
mass, to vvhich all other quantities can be referred. 

UNITS, HEAT— Units based on the quantity of heat re- 
quired to raise a given weight or quantity of a sub- 
stance, generally water, one degree. 

The principal heat units are the English heat unit, 
the greater and smaller calorie and the joule. (See 
Calorie. Joule.) 

UNITS, MAGNETIC— Units based on the force exerted be- 
tween tw^o magnet poles. 

Unit strength of a magnetic pole is such a magnetic 
strength of pole that repels another magnetic pole of 
equal strength placed at unit distance with unit force, 
or witli the force of one dyne. 



429 VIB 

UNITS, PEACTICAL— Multiples or fractions of the abso- 
lute or centimetre- gramme-second units. 



V — A contraction sometimes used for volt. 

V — A contraction sometimes used for velocity. 

VACUUM, HIGH — A space from which nearly all traces 
of air or residual gas have been removed. 

Such a vacuum that the length of the mean free path 
of the molecules of the residual atmosphere is equal to 
or exceeds the dimensions of the containing vessel. 

VACUUM, TORKICELXIAN— The vacuum which exists 
above the surface of the mercury in a barometer tube 
or other vessel over thirty inches in vertical height. 

VARIATION, MAGNETIC—Variations in the value oi the 
magnetic declination, or inclination, that occur simul- 
taneously over all the parts of the earth. 

VARNISH, ELECTRIC— An insulating material dissolved in 

a solvent. 
When the varnish is dry it should produce a layer or 

film of insulating material. 
VIBRATION OR WAVE, AMPLITUDE OF— The ratio that 

exists in a wave between the degree of condensation 

and rarefaction of the medium in which the wave is 

propagated. 

VIBRATION, PERIOD OF— The time occupied in execute 
ing one complete vibration or motion to-and-fro. 

VIBRATIONS, ISOCHRONOUS-Vibrations which perform 
their to-and-fro motions on either side of the position 
of rest in equal times. 



r 



VOL 



430 



VIBRATIONS, SYMPATHETIC— Vibrations set up in 
bodies by waves of exactly the same wave rate as those 
produced by the vibrating body. 

VIS-VIVA — The energ*}^ stored in a movincf body, and there- 
fore the measure of the amount of work that must be 
performed in order to bring- a moving* body to rest. 

VOLT — The practical unit of electro-motive force. 

Such an electromotive force as would cause a current 
ductor which cuts lines of magnetic force at the rate 
of 100,000,000 per sec. 

Such a electromotive force as would cause a current 
of one ampere to flow against the resistance of one 
ohm. 

VOLT-AMMETER— A wattmeter. 

A variety of galvanometer capable of directly meas- 
uring the product of the difference of potential and the 
amperes. 

VOLT AMPERE— A watt. 

VOLTAGE — This term is now very commonly used for 
either the electromotive force* or difference of potential 
of any part of a circuit as determined by the reading 
of a voltmeter placed in that part of the circuit. 

VOLTAIC ARC— (See Arc, Voltaic.) 
VOLTAIC BATTERY— (See Battery, Voltaic.) 
VOLTAIC CELL— (See Cell, Voltaic.) 
VOLTAIC ELEMENT— (See Element, Voltaic.) 
VOLTAMETER— An electrolytic cell employed for meas- 
uring the quantity of the electric current passing 
through it by the amount of chemical decomposition 
effected in a given time. 



431 



VOL 



VOLTAMETER, COPPER— A voltameter in which the 
quantity of the current passing- is determined by the 
weight of copper deposited. 

VOLTAMETER, VOLUME— A voltameter In which the 
quantity of the current passing- is determined by the 
volume of the gases evolved. 

VOLTMETER — An instrument used for measuring- differ- 
ence of potential. 

VOLTMETER, CARDEW'S— A form of voltmeter in which 
the potential difference is measured by the amount of 
expansion caused bj^ the heat of a current passing 
through a fixed resistance. 

VOLTMETER, CLOSED-CIRCUIT— A voltmeter in which 
the points of the circuit, between which the potential 
difference is to be measured, are connected with a 
closed coil or circuit, and which gives indications by 
means of the current so produced in said circuit. 

VOLTMETER, GRAVITY— A form of voltmeter in which 
the potential difference is measured by the movement 
of a magnetic needle against the pull of a weight. 

VOLTMETER, MAGNETIC- VANE -A voltmeter in which 
the potential difference is measured by the repulsion 
exerted betw^een a fixed and a moveable vane of soft 
iron placed wdthin the field of the magnetizing coil. 

VOLTMETER, MULTI-CELLULAR ELECTROSTATIC— An 
electrostatic voltmeter in which a series of fixed and 
movable plates are used instead of the single pair em- 
ployed in the quadrant electrometer. 



//■ 



WAT 



432 



VOLTMETER, OPEN-CIRCUIT— A voltmeter in which the 
points of the circuit where potential difference is to be 
measurefl are connected with an open circuit and gnve 
indications by means of the charges so produced. 

VOLTMETER, PERMANENT MAGNET— A form of volt- 
meter in which the difference of potential is measured 
by the movement of a magnetic needle under the com- 
bined action of a coil and a permanent mag-net, against 
the pull of a spring. 

VULCABESTON — An insulating substance composed of as- 
bestos and rubber. 

VULCANITE — A variety of vulcanized rubber extensively 
used in the construction of electric apparatus. 

Vulcanite is sometimes called ebonite from its black 
color. It is also sometimes called hard rubber. 



w 



W — A contraction sometimes used for watt. 

WALL SOCKET— (See Socket, Wall.) 

WATCHES, DEMAGNETIZATION OF— Processes for re- 
moving magnetism from watches. 

WATT — The unit of electric power. The volt-ampere. 

The power developed when 44.25 foot-pounds of work 
are done per minute, or 0.7375 foot-pounds per second. 
The 1-746 of a horse power. 

WATT-HOUR- A unit of electric work. 

A term employed to indicate the expenditure of an 
electrical power of on« watt, for an hour. 



433 WHB 

WATT-HOUR, KILO— The Board of Trade unit of v/ork 
equal to an output of one kilo-watt for one hour. 

WATT, KILO— One thousand watts. 

A unit of power sometimes used in stating the out- 
put of a dynamo. 

WATT-METET: — A galvanometer by means of which the 
simultaneous measurem.ent of the difference of poten- 
tial and the current passing is rendered possible. 

The w^att-meter consists of two coils of insulated 
wire, one coarse and the other fine, placed at right 
angles to each other as in the ohm-meter, only, instead 
of the currents acting on a suspended magnetic needle, 
they act on each other as in the electro-dynamometer. 

WAVE — A disturbance in an elastic medium that is periodic 
both in space and time. 

WAVE, ELECTRIC— An electric disturbance in an elastic 
medium that is periodic T)Oth in space and time. 

WAVES, ELECTRO-MAGNETIC— AVaves in fhe ether that 
are given off from a circuit through which an oscillat- 
ing discharge is passing, or from a magnetic circuit 
undergoing variations in magnetic intensity. 

WELDING, ELECTRIC— Effecting the welding union of 
metals by means of heat of electric origin. 

In the process of Elihu Thompson, the metals are 
heated to electric incandescence by currents obtained 
from transformers, and are subsequentty pressed or 
hammered together. 

WHEEL, TROLLEY— A metallic wheel connected with the 
trolley pole and moved over the trolley'- wire on the 
motion of the car over the tracks, for the purpose of 
taking the current from the trolley wire by means of 
rolling' contact therewith. 



WIR 434 

WHIRL, EliECTRTC— A term employed to indicate the cir- 
cular direction of the lines of maonetiii force surround- 
ing a conductor conveying an elastic current. 

WHIRL, MAGNETIC— The lines of magnetic force which 
surround the circuit of the conductor conveying- an 
electric current. 

WIXHING, AMPERE — A single winding or turn through 
which one ampere passes. 

Ampere-winding is used in the same signification as 
iimpere-turn. 

WINDING, COMPOUND, OF ]:)YNAMO-ELECTRIC MA- 
CHINE — A method of winding in which shunt and ser- 
ies coils are placed on the field magnets. 

WINDING, SERIES— A ^vinding of a dynamo-electric ma- 
chine in which a single set of magnetizing coils are 
placed on the field magnets, and connected in series 
with the armature and the external circuit. 

WIRE, DEAD, OF ARMATURE— That part of the wire on 
the armature of a dynamo which produces no electro- 
motive force or resultant current. 

WIRE, DUPLEX — An insulated conductor containing two 
separate parallel wires. 

WIRE. FEEDING— A term sometimes applied to the wire 
or lead of a multiple circuit which feeds the main. 

In a system of electric railroads the feeding wires 
feed the trolley wires. 

WIRE, FUSE — A readily fusible wire employed in a safety 
catch to open the circuit when the current is excessive. 



435 WIR 

WIRE, HOUSE— Tn a system of incandescent electric light- 
ing- any conductor that is connected with a service con- 
ductor and leads to the meter in the house. 

WIRE, INSULATED— Wire covered with any insulating ma- 
terial. 

WIRE, IJTSTE — In telegraphy the wire that connects the 
different stations with one another. 

WIRE, NEGATIVE— A term sometimes applied to that wire 
of a parallel circuit which is connected to the negative 
pole of a source. 

WIRE, NEUTRAL— The middle wire of a three-wire system 
of electric distribution. 

WIRE, POSITIVE— The wire or conductor connected to the 
positive pole or terminal of any electric source. 

WIRE. SLIDE — A wire of uniform diameter employed in 
Wheatstone's electric bridge for the proportionate arms 
of the bridge. 

WIRE. SPAN — The wire employed in systems of electric 
railways for holding the trolley wire in place. 

WIRE, TROLLEY—The wire over which the trolley passes 
in a system of electric railways, and from which the 
current is taken to drive the motors on the cars. 

WIRES, DEAD — Disused and abandoned electric wires. 
WIRES, LEADING-IN— The wires or conductors which lead 
the current through (into and out of) an electric lamp. 

WIRES, PILOT— Fn a system of incandescent lightinjgr, 
where a comparatively low potential is employed on 
the mains, thin wires leading directly from the gener- 
ating station to different parts of the mains, in order 
to determine the differences of potential at such points. 



YOK 



436 



WIRES, PRESSUEE— Tn a system of incandescent electric 

lig-hting, wires or conductors, series-connected with the 
junction boxes, and employed in connection with suit- 
able voltmeters, to indicate the pressure at the junction 
boxes. 

The pressure wires are sometimes called the pilot 
wires. 

WIRING— Collectively the wires or conducting circuits used 
in any system of electri'c distribution. 

WORK — The product of the force by the distance through 
w^hich the force acts. 

A force w^hose intensity is equal to one pound acting 
through the distance of one foot, does an amount of 
work equal to one foot-pound. 

WORK, ELECTRIC— The joule. (See Joule). 
1 joule equals 1 watt for 1 second. 

WORK, ELECTRIC, UNIT OF— The volt-coulomb or joule. 
The product of the volts by the coulombs. 

WORKING, PARALLEL, OP DYNAMO-ELECTRIC MA- 
CHINES — The operation of working several dynamo- 
electric machines as a single source, by connecting 
them with one another in parallel or multiple arc. 



YOKE FIELD— That part of the held magnet frame con- 
necting two magnet cores. 

YOKE, MULTIPLE-BRUSH— A term sometimes applied to 
multiple brush rocker of a dynamo or motor. 



437 



ZIN 



ZINC, AMALGAMATION OF— The covering or amalgama^ 
tion of zinc with a layer of mercury. 

ZINC, CROW-FOOT— A crow-foot-shaped zinc used in the 
gravity voltaic cell. 



f 



Y 



INDEX TO TABLES. 

I. Propertues of Copper Wire 13-14 

IT. Currents Allowed in Wires by Fire Underwriters. 16 

III. Electro-eliemical Series of the Elements 20 

IV. Data of Common Batteries 30 

V. Properties of Metals 34 

VI. Permeability Table 57 

VII. Magnetic Traction or Pull 83 

VIII. Magnetic Circuits of Dynamos 91 

IX. Hysteresis in Soft Iron 131 

X. Dynamo and Motor Windings 165-167 

XI. Tensile Strength of Copper Wire 273 

XII. Circumferences of Circles 274 

XIII. Areas of Circles 275-276 

XIV. Areas of Small Circles 277 

XV. Price List Copper Magnet Wire 278 

XVI. Specific Gravities of Metals 279 

XVII. Decimal Equivalents of Parts of an Inch 280 

XVIII. Wire Gauges in Mils 281 



<r 



r 



INDEX. 



Alternating" currents 219 

Alternating- current, advantages of 225 

Alternations 219 i 

Amalg-amation of battery zincs 29 

Ampere turns required in parts of magnetic circuit.. 64 

Ampere turns, calculation of from table 67 

Ampere turns, size of wire to produce certain 105 

Analogy between water and electricity 1 

Anode 31 

Armature current, divis»lon of at brushes 137 

Armature, drum 116 

Armature, gramme ring 113 

Armature, iron clad 66 

Armature reaction 138 

Armature reaction, magnetization of fields by 139 

Armature, smooth core 65 

Armature, tunnel wound . . ^ 50 

Arc lamps. 203 

Automatic rheostat 182 



B 



Battery for experimental purposes 29 

Battery, storage - 35 

Battery, storage capacity of 36 

Battery, storag-e uses of • . 36 



, 



U2 

Batteries, table of data of 30 

Brakes, electric 86 

Brush arc dynamo 139 

Brush arc motor 127 

Brushes, inertia of 190 

Brus'hes, position of in multipolar motors 162 

Brushes, sparking affected by position of 146 







Calculation of ampere turns from table 72 

Canbon brush 148 

Carbon as positive element in battery cell 28 

Capacity of storage batteries 35 

Cafthode 31 

Circuits, primary 227 

Circuits, tsecondary 227 

Commutation, conditions of perfect 146-149 

Commutator, vibration of 190 

Compass, mariner's 40 

Compound winding 170 

Coonpound winding, number of series turns 171 

Connections of armature and field magnets 177 

Constant potential system 20 

Constant voltage, effect on life of lamps 202 

Copper ware, ohange of resistance with tem.perature. . 100 

Counter E. M. F., identity with primary 123 

Current, three-phase 224 

Current, two-phase 222 

Cycle 219 

Cycle, per second 221 



443 



Direction of flow of current 31 

Drop allowed in street railway feeders 18 

Drum armature 116 

Drum armature, winding of 159 

E 

Earth as magnet 40 

Eddy currents 133 

Edison current meter 31 

Edison dynamo, leakage co-efficient of 90 

Electric brakes 86 

Electro-magnet 43 

Electropeon fluid for batteries 29 

Electro-plating 32 

E. M. F., counter 123 

E. M. F., productior of in armatures 112 

E. M. F., winding for different. 117 

Enclosed arc lamps 203 

Energy formulae 95 

Energy in electric circuits 95 

F 

Feeders for street railway work ; 18 

Field coil, improper connection of 196 

Field coil, heating of 196 

Field coil, open circuit in 194 

Field coil, short circuit in 195 

Field discharge 178 

Field, distortion of by armature reactioin 141 



444 



Field magnets 175 

Flow of current, direction of 31 

Force, field of 41 

Force, field of, strength in the U. S 41 

Force, lines of 41 

Force, mechanical, exerted on wire carrying current 

in magnetic field 49 

Friction between brush and commutator 192 

G 

Galvani his discovery 25 

Gramme ring armature 112 

Gramme ring, practical advantage of 116 

Grounds 192 

Grounds, partial 193 

Grounds, permanent 193 

H 

Heating of commutator 192 

Heating of field coils 196 

Heating of magnet coils 108 

H^lix 14 

High voltage, use in transmission of power 99 

Horse power, electrical, equivalent of 95 

Horizontal winding 160 

Hysterisis 130 

Hysterisis in four-pole field 132 

I 

Incandescent lamps, life of 10 

Iron clad armature 66 



445 

L 

Lap winding- 162 

Leads, arm'ature 160 

Leakage of mag^metic lines 89 

Lentz law 119 

Life of incandescent lamps 10 

Lines of force 41 

M 

Magnet, electro 43 

Magnet, field of 45 

Magnet, best design for lifting purposes 84 

Magnet coils, calculation of 106 

Magnet coils, heating* of 124 

Magnetic lines, bunching of 69 

Magnetic tractio'n 82 

Magnetic lines, leakage of 89 

Magnetic spectrum 42 

MagiUetic wihirl 42 

Magnetic vane volt meter 214 

Magnetism 40 

Magnetism, residual 213-175 

Mag"netization of fields by armature reaction 139 , 

Maniner's compass 40 

Mechanical force exerted in wire carrying* current in 

magnetic field 49 

Meter, Brush 213 

Meter, Thompson's recording 215 

Meter, Westinghouse 214 

Meter, Western Electric 212 

Meter, Weston 211 



446 

Motor, Baxter 127 

Motor, Brush 127 

Motors, compound wound 170 

Motor, series and properties of 125 

Motor, shunt wound, speed of 124 

Motors 208-211 

Multipolar field, effect of on armature reaction 140 

N 

Nitrate of soda as electrolyte 28 

Number of bars in commutator 164 

Number of slots in armature 164 

Noise of machine in operation 197 

o 

Ohms law ' , 3 

Open circuits 186 

Open circuits in field coils 194 

Over commutation 147 

P 

Periodicity 221 

Permeability 56 

Platin-g- electro 32 

Platinum sponge 27 

Platinum wire in incandescent iamips 202 

Polarization 26 

Porous cup 27 

Poly phase currents from direct current commutators 224 

I'ositiion of brushes in multipo'lar machines 162 



U7 

Power from primary batteries 28 

Primary circuits 227 

R 

Residual magnetism 175 

Kesistance of brush contact 147 

Eesistance of copper wire, change of with temperature 106 

Resistance of copper wire, rule for 20 

Revolving pole 224 

Rheostat 177 

Rhumkorf coil 228 

s 

SiUuration of magnetic circuit 56 

Secondary circuits 227 

Self induction 145 

Series arc lamps ^ 205 

Series system of arc lighting 20 

Series wound motor, properties of 125 

Short circuits 187 

Shunt motor proper, connection of 181 

Shunt wound motor, constant speed of 124 

Sine wave 221 

Smee battery 27 

Smooth core armature 65 

Solenoid 45 

Solenoid meter 216 

Solid pole pieces, eddy currents in 134 

Sparking 144-189 

Spectrum magnetic 42 

Starting box, automatic 182 



r 



448 



Starting box, overload 183 

Steel ingt>ts handled by means of magnet 86 

Storage batteries 35 

T 

Thompson recording meter 215 

Three-phase current 226 

Transformers 227 

Transmission of power by alternating currents 228 

Traction magnetic . . .* 82 

Tran'smission of power, connection with high voltage. 98-99 

Transmission of power, weight of copper 09 

Tungsten steel 210-40 

Tunnel wound armature 50 

Two phase current 224 

V 

Vacuum 201 

Vertical winding 160 

Voltage comstant, effect on life of incandescent lamps 202 

Voltage of storage battery 4 

Volta's battery 25 

Voltameter i 31 

Volt-meter, Weston 207 

w 

Watts, mechanical equivalent of 95 

Watts, radiated from armature 106 

Watts, radiated from field coil 107 

Watts required for incandescent lamps 203 



449 

> 

Wave sine 221 

Wave winding 161 

Weston meters 207-208 

Winding's, armature 165 

Winding lap 162 

Wire winding, armature, arrangement of 158 

Wire on dynamo, office of 157 

Wiring for equal drop 17 

Wood sure dynamo 139 



> 
«» 



LB D '05 



